“Mort and I are far from retiring,” Lynn Nesbit said on Friday afternoon. “It isn’t a question on the table at the moment. It really isn’t.”

The night before, one of the stars at the boutique literary agency Ms. Nesbit runs with Mort Janklow abruptly announced that he was leaving for a job at the global, multiplatform talent agency William Morris. Eric Simonoff, who represents Pulitzer Prize-winner Jhumpa Lahiri and others, had spent 18 years at Janklow & Nesbit. Apart from a stint as an assistant at Norton the year after he graduated from college, it was the only job he’d ever had. At 41, he was widely thought to be the prince of the firm, in line to one day take over for Ms. Nesbit and Mr. Janklow alongside his equally heavy-hitting colleague, Tina Bennett.

Precisely what such a takeover would potentially entail depends on who you ask, but until last week, the consensus assumption among publishing people was that the agency’s namesakes, 78-year-old Mort and 70-year-old Lynn, had been deliberately grooming Mr. Simonoff and Ms. Bennett, and would hand the reins to the agency over to them when they got tired of steering it. 

Because of this, many found Mr. Simonoff’s sudden defection puzzling, and the motivations behind it have been intensely debated.

Though Mr. Simonoff could not be reached for comment, Ms. Nesbit said Friday it wasn’t really so complicated at all.

"I think what provoked him is the huge financial offer,” she said. “I think it’s as simple as money. He said they made him an offer he felt he could not refuse.” 

She added, “He’ll be the only alpha male in William Morris's literary department.”

Suzanne Gluck and Jennifer Rudolph Walsh, co-heads of the William Morris literary department, announced their new hire on Friday just as all of publishing prepared to pack into the New School’s Tishman Auditorium for the National Book Critics Circle Awards. The news appeared on The New York Times’ ArtsBeat blog under the headline, “A Star Book Agent’s New Home.” Therein, Ms. Gluck was quoted as saying Mr. Simonoff had been her “dream date” for years.

Three well-placed sources who would not speak for attribution said Ms. Gluck and Ms. Walsh (neither of whom would comment for this article) had been actively looking to add someone of Mr. Simonoff's stature to their ranks for several years. Several industry people—knowledgeable ones, the lot of them, though obviously all too shy to speak on the record—said William Morris could use someone with literary sensibilities who can hit home runs with titles that skew more commercial than the high quality (but often narrowly targeted) stuff that Bill Clegg tends to do.

Publishing people were giddy when they heard about Mr. Simonoff's job change last week, and not even because they were happy for him—though some were—but because it was surprising, and exciting, and an undeniable show of force by William Morris that no one really knew how to explain off the top of their heads. Editors, publishers, agents, everyone wanted to talk about it, and they got into work on Friday still drunk on the news and excited to start calling and emailing one another about it. People asked if a “dominant theory” had emerged, the question invariably coming out sounding hopeful, but also cautious, because no one really wanted the fun to end.

The last time anyone felt this way was in June, when News Corp. fired Jane Friedman. With all that had happened since—the wrenching reorganization of Random House, the closing of Collins—that felt like a lifetime ago. 

"Was I shocked? No,” Ms. Nesbit said on Friday. “I was surprised but not shocked. I think Eric has to spread his wings. Maybe it was all too much like family."

But what exactly was behind Mr. Simonoff’s defection? His colleagues in the industry were left scratching their heads over the weekend.

“There had to have been something material that prompted it,” one editor said. “It’s not something you would do just for the sake of it ‘I just want a change’— agents don’t do it.”

Was it as Ms. Nesbit said? Had William Morris just offered Mr. Simonoff a dizzying amount of money? Or was there more at work—like, say, unresolved succession issues at Janklow & Nesbit that might have caused the famously ambitious agent to lose his patience with the firm and seek out something more secure? 

In a sense, there are two stories here, one about why Mr. Simonoff is joining William Morris, and the other about why he is leaving Janklow.

One theory is that he was tempted by all the perks that come with working for a large multimedia talent agency—namely, access to in-house film and TV agents who can help him not only by selling his adaptation-ready literary properties but also by giving him business whenever one of their celebrity clients wants to write a book.

In an interview Friday, former William Morris literary head Owen Laster, who retired from the firm after 46 years in 2006, said many of the opportunities a large organization with many branches offers are simply not possible at a small, prestige shop like Janklow & Nesbit. He offered that when he was agenting at WMA, he “personally handled many film and television deals” for his clients, and “very often” collaborated with people in other parts of the company.

“That office [Janklow & Nesbitt], although primarily literary, has a pretty wide base, but not like William Morris,” Mr. Laster said. “Their connection with CAA and other offices gives them power in those areas, but at William Morris it’s more direct—it’s our clients.” 

While the possibility of multimedia domination may have certainly appealed to Mr. Simonoff, the real reason behind his decision to leave his longtime home probably had a lot more to do with the murky question of succession at Janklow & Nesbit and the sense of uncertainty that is clouding the agency’s future. 

For one thing, Mr. Janklow is said to have thought seriously about selling the company over the years—and though he has denied it, he has reportedly put a price tag on it that was rebuffed by potential buyers. For another, there is the matter of Mr. Janklow’s 41-year-old son Luke, a former rock singer and current restaurant owner who has in recent years been doing some agenting for his father's shop, and Ms. Nesbit’s daughter Priscilla Gilman—a recovering English professor who recently returned from a nine-month leave of absence during which she wrote a memoir about motherhood.   

Did the presence of the young Mr. Janklow and Ms. Gilman signal to Mr. Simonoff that the agency would always remain a family business? That all the loyalty in the world wasn’t going to make it any more likely that he'd ever be made partner?

Nonsense, according to Ms. Nesbit: “I don’t think it was about succession," she said. "I honestly, genuinely do not think it was about that."

"I think Luke has many strings to his bow,” she added, referring to the young Mr. Janklow’s various non-literary pursuits, which also includes collecting guitars and cars. “I have a very strong alpha male here, you see, in Mort Janklow. Eric felt more comfortable with another younger guy here. I don’t think Luke and Priscilla were in any way a threat to him.”

Regardless of why it happened, Mr. Simonoff’s departure unmistakably leaves Janklow & Nesbit with a future even more uncertain than the one it was already looking forward to, especially considering that whatever finally convinced Mr. Simonoff to flee could conceivably convince Ms. Bennett to do the same.

Several people noted that Ms. Bennett and Mr. Simonoff are the only major players at the agency bringing in new clients and making spectacular sales with any regularity (Update, 5:15PM: It should be noted that just two weeks ago, Ms. Nesbit placed the journalist Andrew Meier's The House of Morgenthau with Random House, and before that sold a memoir by young Iraq veteran Christopher Brownfield to Knopf). Mr. Simonoff has Ms. Lahiri and Edward P. Jones, for example, and in January, he showed his muscle when he sold Danielle Trussoni’s debut novel Angelology in a hotly contested auction for nearly $1 million. Ms. Bennett, in turn, represents Malcolm Gladwell, Fareed Zakaria, Laura Hillenbrand, Eric Schlosser and many others. Sure, the elder Mr. Janklow can still do a multimillion-dollar eight-book deal for Danielle Steele with his eyes closed when he wants to, and Ms. Nesbit is still putting up dizzying numbers with her Tom Wolfe and her Anne Rice sales. But as one publisher put it, “they’re not taking on new people. What’s the future?” 

That publisher, along with other executives, speculated on Friday about whether Mr. Simonoff’s departure might inspire Ms. Bennett to look for other work, or whether it would instead have the effect of forcing some of the succession issues at the agency to the fore.  

Though unlikely, Ms. Bennett could conceivably follow Mr. Simonoff to William Morris. Said one knowledgeable agent, “Jennifer Walsh used to say, 'I'll get Tina Bennett over here—Watch me.’”

Ms. Nesbit sounded cool as a cucumber when confronted with that scenario Friday. "I expect Tina to be here forever,” she said.

Ms. Bennett declined to comment for this article.

Women on horseback heading to or from the Claremont Riding Academy: This summer, it's a sight that's bound to evoke an emotional reaction-and not just because it reminds you that classic New York is soldiering on through yet more tough times. Something primal and powerful is going on between the people of this city and horses. Quite simply, a mere glimpse of those strong, those brave, those magnificent beasts is enough to do us in.

From the tear-soaked blockbuster-to-be Seabiscuit to Tony Soprano's late, lamented racehorse, Pie-o-My, to plucky New York–bred Triple Crown contender Funny Cide, to first daughter Georgina Bloomberg's showhorse, Action, horses are taking us all out for a much-needed joyride.

Nowhere is the love of horses thrown into such stark relief as at that not-so-gracefully-aging landmark Claremont, with its pint-sized indoor ring, its pungent manure odor, its workaday-looking horses craning their necks out of rickety upper-story windows-and its overwhelmingly female clientele. It's the only riding stable left on the island of Manhattan, and there's nothing fancy about it. No one rides there in order to improve her social profile or-what often seems like the same thing-her status as a serious rider. For that, there are tiers and tiers of stables out on Long Island and in Westchester, where prominent New Yorkers like Kelly Klein and socialite Sale Johnson keep their pricey equine love-objects, caring for them, training and competing on them with the wild devotion of medieval alchemists.

But let's consider horses in New York City for a moment. They may be an eternal symbol of the leisure class and its luxuries, but horses still evoke an old New York that's both refined and gritty-one part House of Mirth, one part The Alienist. The "21" Club, the horse-drawn carriages that amble through the park and the Metropolitan Club's courtyard, formerly used by horses-sure, they're all anachronistic, but far from being pointlessly nostalgic, they're actually uplifting. Who would erase these last, poignant vestiges of urban horsiness?

So it can only be a good sign, a hopeful sign, that New York horse culture is having a moment, with New York gelding Funny Cide winning the Kentucky Derby and the Preakness (only to be foiled-what classic tragedy!-in our own Belmont Stakes), the Mercedes Benz Polo Challenge in the Hamptons established as a de rigueur stop for anyone with social ambitions, and Tobey Maguire in Seabiscuit poised to warm hearts and jerk tears all over town. The Manhattan previews of the movie based on Laura Hillenbrand's 2001 best-seller were virtual sobfests, with audiences shedding as many unembarrassed tears at the happy parts as at the sad.

Forgotten are the days of the horse-insurance frauds of the mid-90's, which scandalized the racing industry and dirtied the reputations of leading equestrian families like the Lindemanns, the Wards and the Vallieres. Gone, too, are the old establishment boundaries of horse culture. Things have moved beyond the backyards of the Whitneys, Phippses and Vanderbilts. The owners of Funny Cide-a group of high-school friends, most of whom were in the construction business in Sackets Harbor, N.Y.-are advertisements for hard work, perseverance and humble but steady ambition.

But it's the emotion behind horse-human relationships that is blooming most conspicuously. With men, as always, it's centered on the racetrack-think of Tony Soprano weeping over the death of his racehorse, and then avenging it as if the animal were his own child. With women, it's all the other equestrian sports that have the pull, as another Sopranos connection shows: 17-year-old Stella Keitel, daughter of Lorraine Bracco, has been showing her aptly named horse, Bada Bing, all over the East Coast. Keeping her company are Jessica Springsteen, daughter of Bruce; Paige Johnson, daughter of BET founders Sheila and Robert Johnson; and Daisy Johnson, daughter of Johnson & Johnson heir Woody Johnson and socialite Sale Johnson, who is also a rider and stable owner herself. Glenn Close's teenage daughter, Annie Starke, also has a horse, and Mayor Michael Bloomberg's 20-year-old daughter Georgina is an avid rider-she even has her own "Rider Insight from Georgina Bloomberg" Web site.

The sport's female profile is not lost on Paul Novograd, the owner of Claremont. "It's a great place for a bachelor," he said, and offered a few theories of his own about the love affair between women and horses. "Girls are just fascinated by horses, by their strength and power and their vulnerability. I think the fact that these big, strong, powerful animals are so timid and need to be treated so gently elicits a positive response among women, whereas guys just want to break them." At Claremont, women come for lessons as early as 6:30 a.m. "A lot of people want to get their equine fix before work," said Mr. Novograd. He has to buy horses that are, above all, capable of making it in Manhattan. "It's not every horse that's cut out to be a city slicker," said Mr. Novograd. A half-hour private lesson costs $60. The status associated with the sport, Mr. Novograd said, "is in the eye of the beholder. Some people think they are quite something because they ride horses."

While Mr. Novograd claims that his clients include diplomats and fashionistas, what social clout Claremont has doesn't even skim the surface of the horse culture flourishing outside the city-the glistening lawns of the Hamptons horse shows, the sparkling floors of Bedford barn tack-rooms, the flower-lined jump courses surrounding Westchester's indoor arenas.

Ms. Johnson, who is in her 50's, and Ms. Klein, 47, own barns that churn out champion show horses. Media fixtures such as Maurie Perl, the head Condé Nast spokeswoman, and Brandon Holley, the editor of Elle Girl, call horseback riding their "addiction." And their passion goes beyond the $100,000 price tags on their animals and the trophies that line their tack-room walls. "I think girls are fascinated by horses from a very young age," said Ms. Holley. Just as she began riding because of International Velvet, she thinks that now, pony sales will go up because of Seabiscuit. "Girls grow up fantasizing about owning a horse; they read Misty of Chincoteague, Black Stallion, Black Beauty…. Boys like Tonka trucks." Ms. Holley thinks of it as an escape. "I look at extreme mountain-biking. If you want to know an extreme sport, it's going over a 4-foot-3 oxar, turning and going over a 4-foot-3 vertical."

Women will do anything to keep at it. Ms. Holley also describes it as an endless money game. "The whole thing is just in search of a better horse. You marry to feed the addiction," she said, only half-joking. According to Ms. Holley, the best part is "training and working with an animal that closely. The horse has to trust you to get him to the fence. It's definitely a partnership." Unlike an owner-pet relationship, a horse is more interactive. "The horse can get sick of you, too," she said. "If the horse sours on you, you're in trouble. The horse isn't running at you with its tail wagging. You have to spend that time to build that relationship, especially when you find that one horse that can take you. For me, it takes a year to get to know a horse. To build that level of trust and knowing, I have to ride very firmly," she said. While she admitted that people ride for status reasons, because it's "prohibitively expensive," she added that "the whole culture just sucks you in."

Ms. Perl didn't start riding seriously until she reached her 30's, but she was immediately hooked, and now has two horses of her own, Starlight and Lucky, both of whom she keeps up in the Berkshires. "Riding is the one thing I do for pure joy and pleasure, something that I say is mine," she said. "I think I love the physicalness of riding." Ms. Perl doesn't compete, calling riding "the one thing in my life that I have absolutely no wish to be competitive in. I have enough of that." She likens the sport to animal therapy: "I've gotten a lot stronger through the riding. You have to pull through the fear. It's about taking care of yourself and taking care of your animals. I like the animal, I like being near the animal. I go to the barn very, very tense, and I leave the barn much calmer, with a smile on my face all day." She said her trainer taught her how to separate her work life and her outside life. When she was working at The New Yorker, and Jeffrey Toobin's explosive story about O.J. Simpson and his incriminating glove was about to come out, Ms. Perl was at the horse farm riding Lucky. She kept getting cell-phone calls from her office, until her trainer finally told her to choose one or the other: stay on her horse and focus, or dismount and take her calls. Fortunately for the magazine, she chose the latter. She feels the same affinity to her horses as Seabiscuit's trainer, Tom Smith, felt for his. "You can't hug a horse the same way you can hug and cuddle a dog, but I think horses are very intuitive animals, and they are sensitive," Ms. Perl said. "[Lucky] took care of me. If I didn't give him the proper signal, he wouldn't do things if he wasn't sure I could do them. If I didn't center him up for a fence, he'd center himself up." Riding, she said, "makes you get out of yourself," adding that women ride "because they love the animals. They're so beautiful and so graceful. They look at them not as a pet, like a dog or cat, but in a more emotional way. Men ride more as a sport."

On the high-profile A-rated horse-show circuit, the equestrian world lives out its tony, competitive reputation most fully. On the East End of Long Island, the barns that matter are Sag Pond, Swan Creek, the Topping Riding Club, Meadowview and Two Trees, all in Bridgehampton, and Rosehill, in Southampton. These stables draw the city's elite out to work with the best trainers in the business. In Seabiscuit the book, Laura Hillenbrand says that riding evokes Hemingway's idea about bullfighting-it's the only place where you're "all the way up." In the Hamptons and the rest of the East Coast horse-show world, riders are "all the way up" in many ways-in status, in adrenaline and in the money they shell out. The fee just to enter an A-level show is typically $500, and stable fare and truck fare can add up to $2,000. An outfit alone can cost over $1,000, not to mention $800 custom riding boots. Jackets are about $500, and jodhpurs are $150.

But those are only the basics, the minimum. Even more important is having an animal who picks his knees up high enough, has the right confirmation and the right pedigree. The range for such a horse is $50,000 on the low end to several million dollars for Grand Prix jumpers. Another must is having the right trainer and riding out of the right barn. An hour lesson is about $100 on your own horse, and boarding a horse at Topping Riding Club is about $1,500 a month. All told, having a daughter who rides costs about the same as educating her in private school. Or, in some cases, many times more: Allison Firestone-cousin of the Bachelor, daughter of Mr. and Mrs. Bertram Firestone-rides a $4 million horse named Jox in the Grand Prix.

When a young girl gets her first hankering for the riding world-when she is ready to move past pony rides at birthday parties and knows she wants to compete-it's only the beginning. From age 5, she competes in lead line, where a parent or trainer leads her around the ring in a line of other tots on horseback. Gradually she learns to jump, and jump higher. She schools for hours on end on hot summer days, jumping over rolltops, water jumps and brightly colored oxars. Her love for her horse turns into a love for all things horsy-and then, eventually, for more and more horsies. Every year, after all, she grows, meaning she needs the next-sized horse or pony. Once she hits her mid-teens, if she wants to be really competitive, she needs multiple horses-one for schooling, one for the jumper division (timed), one for the equestrian division (judged on the rider) and one for the hunter division (judged on the horse).

For most of a young girl's career, though, she can remain blissfully unaware of the cachet of her sport. She has eyes only for her horse and for the next obstacle in the course. For her, it's all pretty straightforward: The status game comes in the form of the ribbons she wins, her rank in the zone, whether she makes it or not to the end-of-the-year nationals. She may not be racing, but she feels the same pumped-up anxiety as Red Pollard in Seabiscuit, the same urge to conquer the course ahead of her, the fear that she will not perform, that her horse will not perform, or that they will perform out of sync. She enters the show ring at the Hampton Classic unaware that Alec Baldwin could be standing along the sidelines, that Vogue is doing a cover shoot in the grassy pasture beyond, or that the Mayor's daughter could be entering the ring behind her. She doesn't realize that the dirty, dusty sport she has practiced all her life could actually be fashionable-until she sees odd imitations of her riding gear in the windows of Dolce & Gabbana, stands in the Hampton Classic V.I.P. tent on Grand Prix Sunday watching the New York Post and Daily News snap photos of Calvin Klein and Billy Joel in front of her, and then takes in a polo match with the Bush daughters down the road at Bridgehampton's Two Trees Stables.

At all these places, she notices a funny thing-the absence of the actual animal. Along Madison Avenue, the tall boots in the window that cost $4,000 could never be worn on a horse; twice around the ring would give the rider a saddle sore that would sting for weeks. On Grand Prix Sunday, the Christie Brinkleys and Linda Evangelistas aren't even watching the 1,500-pound beasts hurling themselves over triple oxars at record speeds unless they happen to make up the background of a photo shoot. At the Bridgehampton Mercedes-Benz Polo Challenge, Paris and Nicky Hilton and Lauren Bush sip their Moët and keep their Jimmy Choos far away from the manure-covered polo field.

The horse world, in short, can be a haven of a certain kind of purity for certain upper-crust women. Though they are often celebrities or relatives of celebrities, or they live off Further Lane, the actual competitors who own and ride their own horses forget about social status when they're in the ring. They are so focused on the equine side of things that they think of their horses almost as members of the family. Kelly Klein, Calvin's former wife, has ridden horses since she was 4. She shows two-Oz, a large chestnut, and Elstar, a bay gelding with a perfect white diamond on his forehead-and houses her retired horses, "some babies" and "some up-and-coming horses in training" on her Bridgehampton farm, Wild Ocean.

"When I was a little girl, I just fell in love with them. I became very much attached to the animal," she said. "It's a hobby, but when you do it at the competitive level, it's much more of a discipline-it takes a lot of hours and work. Every day the animal is different," she added. Ms. Klein said she became addicted to the sport because she found, "when I'm with them and riding them, I don't think about anything else. It's very good therapy. For me, they are my big pets. I treat them like that. They're different than a dog; you can't train them in the same way. You train them in other ways that give you a real pleasure." Ms. Klein said her horses were like people: "Some are very confident, some are very athletic, some are frisky, some are very relaxed and some have an attitude problem."

To understand the rider's relationship with her horse, she gushed, "go see Seabiscuit. It tells you the whole scenario of the way the horse can be. They try to please you. You know how it is with a dog-well, with a horse, it's 50 times more." After Seabiscuit, she said, there's bound to be a big comeback in the race-horse business. Ms. Klein appreciated the movie showing the time and training and effort involved in riding a horse. "It's the same way with my horses. Maybe showing up one day at the Hampton Classic and dressing up is a really fun event, like showing up for the Kentucky Derby, but I think people who actually own show horses and compete are not doing it for any status. They're doing it for the love of the animal, to compete, to train and to win," she said.

Ms. Klein bought her farm, Wild Ocean, in 2000 with her longtime friend and riding competitor, Stormy Byorum, chief executive of Cori Investment Advisors, a new investment bank. Ms. Byorum was inspired to ride by a clip with Jennifer O'Neill galloping down the beach bareback. In her late 20's, she decided to take a few lessons at the prestigious Topping Riding Club in Bridgehampton. "I became quite intrigued and passionate about it," she said. "I started from nowhere, kept going, bought a horse, went to a horse show, bought another horse." She and Ms. Klein brought in Charlie Weaver, who had been their trainer for over 15 years, from Old Salem Farm and came to Bridgehampton in the summertime, where they rented Dark Horse Farm and eventually bought the farm next-door on Mitchell Lane, which they named Wild Ocean. There, she and Ms. Klein each have five horses they keep in the Hamptons in the summer. Then they ship the show horses to Palm Beach, where they ride in the Wellington circuit. Her newest horse is named Broadway. "He had me at hello. He's my new baby in town," she said.

"Riding is really relaxing to me," said Ms. Byorum, who attends six or seven horse shows each winter in Florida and five in the summer. "It's a very maternal thing, too. Neither Kelly or I have kids. Horses may be 1,500 pounds, but they're still babies." Ms. Byorum will again be entering their horses in the Hampton Classic. Again she will manage to wake up on Grand Prix Sunday at the crack of dawn, lead her horses around 3-foot-9 obstacles competing against the best horses in the world, and manage to make it to her table under the V.I.P. tent to entertain a dozen guests at the day's main event. Ms. Byorum thought Seabiscuit showed the dedication necessary to excel in the sport. "All the people in the horse world read it two years ago," she said. "Riding is emotional. I can't tell you how much. This is not just for spoiled rich people. People don't do this just because there's nothing to do in the afternoon."

From the hundred thousand fans this year at Belmont sloshing through the rain with their kegs and coolers to watch Funny Cide, to the bug-eyed face of Tobey Maguire pushing his horse down the Santa Anita race track, the equine love affair has moved beyond the brims of the wide straw hats in the Belmont sky boxes. It's worth remembering, too, that it was the passion of a writer, Laura Hillenbrand, who recently revealed in The New Yorker that she battled chronic fatigue syndrome to write the book, that revived the half-forgotten cult of Seabiscuit in the first place. Other authors are soon to follow in Ms. Hillenbrand's path: Michael Korda, the horse-loving editor-in-chief of Simon and Schuster, is coming out with a memoir called Horse People in the fall, and Putnam just contracted Sally Jenkins to write a book about Funny Cide. Oon the page as well as in the flesh, horses live on as vividly as ever.