The day, December 21, 2011, had started out normally as he left the kind of home - sweeping curved staircase, perfectly plumped chintz pillows, backyard swimming pool and a Ferrari in the garage - that makes many New Yorkers deeply jealous, and headed to the steel-and-glass tower in midtown Manhattan where he directed the firm's bond business.

In the afternoon, he hosted a charity auction in the city to benefit sick children. That night, he attended a Morgan Stanley holiday party at the swanky rooftop bar at Ink48 Hotel. When he left the party, he looked for the black town car that was supposed to take him to his $2.7 million mansion in the wealthy enclave of Darien. He couldn't find the car, so he hailed a yellow cab.

In less than two hours, what allegedly began as a tussle over a cab fare, which the taxi driver said was $204, led to a struggle that could cost Jennings his career.

On March 9, Jennings walked quietly into a Stamford courtroom and pleaded not guilty to charges of assault, larceny for not paying the fare and intimidation with racial slurs against Mohamed Helmy Ammar, an American citizen who was born in Egypt. The proceedings took just a few seconds. Jennings, dressed in a navy blazer, white shirt and royal blue patterned tie, left swiftly afterwards with his lawyer, Eugene Riccio, followed by a noisy throng of reporters and photographers.

If convicted of all three charges, Jennings, Morgan Stanley's head of fixed income for North America, could face up to 11 years in prison. First-time offenders rarely face such stiff sentences but the charges are serious, and both Jennings' job and reputation are at stake.

Morgan Stanley has already placed him on leave. The firm's spokesman declined to comment, other than to say no decision has been made regarding Jennings' longer-term status at the firm. One top-ranking Morgan Stanley executive, though, said he "does not stand a chance of getting his job back."

Jennings may also face a civil suit for damages from the taxi driver. Ammar's attorney, Hassan Ahmad, says no settlement discussions are taking place, but his client is talking about such a suit.

"Our client wants justice,'' Ahmad said. "He wants Mr. Jennings to be prosecuted to the full extent of the law."

A pre-trial hearing is set for April 12.

CONTRASTS

There are some parallels between this story and Tom Wolfe's 1987 fictional bestseller, "The Bonfire of the Vanities," in which bond trader Sherman McCoy and his mistress hit a Bronx high schooler with his Mercedes, then flee the scene. He is eventually tracked down by the police and is arrested after a campaign by a newspaper.

At first glance, Jennings seems an incarnation of Wolfe's "Master of the Universe" stereotype. He is in the bond business. His two children attend one of the best private schools around. His home is a set piece for the good life, with sisal carpets, marble floors and state-of-the-art appliances. The backyard boasts a children's paradise of playthings as well as a fire pit and posh entertainment center.

Ammar and his family, in contrast, live in a ground-floor apartment in Astoria, Queens, in the shadow of the Triborough Bridge, a home where Amtrak Acela trains rumble constantly overhead. The most striking thing about their yard is the mass of thick black cables snaking out the windows to satellite dishes on the roof. Rust bleeds from the lime-green vinyl siding. The communal garbage cans are penned within a rusty, two-foot fence beneath his living room window.

But while Wall Street's Masters of the Universe certainly still do exist, Jennings apparently wasn't one of them, according to several colleagues. And though at first Ammar was something of a tabloid celebrity, garnering publicity like supporters of Wolfe's hit-and-run character, he's no longer talking to the press, and is telling friends and family not to tell his story either. It's hardly the media-fueled firestorm that erupts in Wolfe's novel.

Ammar agreed to be interviewed for this article. Jennings did not and his motive for the alleged stabbing remains unclear. His attorney, Eugene Riccio, declined to comment, though he has said elsewhere that his client views the incident as an "abduction" and that Jennings denies using racial slurs.

"MORGAN MONK"

Based on interviews, police reports, media accounts, court filings and affidavits, here is what we know about the two men and the incident that, in a few minutes, changed both of their lives.

William Bryan Jennings was born on December 19, 1966, the son of Judith and William C. Jennings of New Canaan, Conn. BJ, as he is sometimes called, went to New Canaan High School, and majored in political economy at Williams College, where classmates say he didn't stand out much. In a cliquey school, he hung "with the hockey guys," says a friend who asked not to be named. When they saw newspaper pictures of him after his arrest, some say they were surprised. He looked 55, not 45. It was the product, they surmised, of his workaholic ways and a job that demanded rising at 4 or 5 a.m. weekdays and clocking in on weekends and holidays.

Jennings got an MBA at Northwestern University's Kellogg School of Management, then joined Morgan Stanley's investment banking division in 1993, and climbed steadily. In 2001, he married Barnard College grad Lee McGill.

In the world capital of ego-driven alphas, Jennings didn't come off as one. He was polite and well-liked, according to Morgan Stanley colleagues. He also was a "Morgan monk," utterly devoted to the firm and his job, with little personal life outside work. He was one of those guys, colleagues say, who bled Morgan Stanley.

A senior employee who worked directly with Jennings said he is "very mild-mannered and very professional." The employee said Jennings is "more stuffy than me" and has dealt with a lot with treasurers and chief financial officers. "He's not some kind of lunatic."

Mohamed Ammar has little time for life outside of his family, his cab and his prayers five times a day. Like Jennings, he toils away - working six days a week.

Ammar was born a world away in Egypt, on January 15, 1968. His father taught Arabic in high school and Mohamed, who had four sisters, grew up in a middle class neighborhood in Sadat City, about 60 miles (100 km) northwest of Cairo. He graduated in 1990 with a degree in accounting from Minufiya University, one of the largest public universities in the country. But Ammar was restless to see the world.

He set out for Amsterdam, lived with a friend and learned to speak Dutch "almost perfectly," he says. When he arrived in New York, in 1994, he had no real plans. He simply enjoyed being on the move. His first job was manning a flower stand on 1st Avenue and East 7th Street in Manhattan. He was terribly homesick, but his friends urged him to stick around. "The future is here!" Ammar says they told him. So he toughed it out.

One day, a woman wandered up to his stand, looking for flowers for her son's summer camp teacher. The two chatted. She gave him her number, because he didn't have a phone. He called her. That weekend they had dinner at an Egyptian restaurant in the Village, and again the following weekend. She was his first girlfriend. They were married in an Islamic ceremony at a Brooklyn mosque in 1996, and later that year got a marriage license at City Hall. He moved in with her in a three-bedroom apartment on the Grand Concourse in the Bronx.

Ammar took a job working in the deli section of a Trade Fair supermarket in Queens. After a year, the low pay and a long commute wore him down. His friend from the flower stand had some advice: "Get a limo license. You don't even need to buy a car."

He began driving for Tel-Aviv Car & Limousine Service in 1998. His grueling hours strained the marriage. By 2001, he was divorced. After 9/11, the limo business tanked as corporate accounts dried up. Drivers were laid off. Ammar, having a hard time making ends meet, returned to Egypt, where he met his second wife, Raina, through family. They were married in Sadat City in 2002, and over the next few years had three sons.

To make money, Ammar returned to New York without his wife and got a taxi license. He traveled between the two countries for several years. Working nights driving a cab, he pulled in $800 to $1000 a week. In 2007, Ammar obtained U.S. citizenship and brought his young family to the two-bedroom first-floor apartment in Queens where the trains roar overhead.

Ammar began December 21 like any other working day. He rose around 2 p.m. to prepare for his regular 4 p.m. to 4 a.m. shift. He made coffee, prayed as usual and gathered three bottles of water from a case he keeps cold on the windowsill of his apartment.

DRINKING

As Ammar began his shift, Jennings had just kicked off the auction for the Manhattan children's hospital. The event, at a venue near 48th street on the west side of Manhattan, was rich with items to bid on: pro sports tickets, weekends at five-star hideaways, dinners with the rich and fabulous. It would eventually raise $50,000. As the room hummed and buzzed, Jennings drank two or three Coors Lights, according to his statements to police.

Shortly after 6 p.m., as the bash wound down, Jennings walked across the street to the Morgan Stanley holiday party. The party was at the rooftop bar of the Ink48 Hotel, known for its leggy waitresses, bed-like rattan sofas and the panoramic views of Manhattan. Jennings said he had several more beers.

It was around 10:30 when Jennings left the party. After searching for ten to fifteen minutes, he couldn't find the black town car ordered to take him home.

So he flagged a yellow cab. Mohamed Ammar pulled over.

Ammar said he thought Jennings, who was wearing a white shirt and olive coat, was drunk, according to the police report. The taxi driver said he and Jennings agreed at the outset that the fare would be $204, the amount dictated by the Taxi & Limousine Commission for the 43-mile journey to Darien. Jennings claims they never agreed on a specific fare amount.

Almost immediately, Jennings asked to pull over because he was hungry. Ammar stopped at the G&G Deli off 10th Ave in Manhattan, where Jennings bought a 20 oz. bottle of Aquafina water, a sandwich and some Burger King cheesy fries. When they resumed the trip, Jennings asked Ammar to wake him up at the Darien exit, then slept for 30 minutes. When Ammar woke him, Jennings gave directions to his house instead of supplying a street address.

Accounts differ on what happened when the cab pulled into Jennings' driveway shortly after midnight. Ammar says he asked for the $204, and that Jennings balked and said he'd give him $50. Ammar says he tried to call 911 from Jennings' driveway, as the TLC advises when there's a fare dispute, but that there was no cell phone service.

Jennings says Ammar demanded $300 and that Jennings offered $160 instead. "I believed that he was trying to take advantage of me," said Jennings in a written report he submitted to police nearly a month later, on January 20.

Both men agree about what happened next: Ammar backed out of the driveway and headed through town. Ammar says he told Jennings he was going to find the police. He alleges Jennings sneered that the police wouldn't do anything, because I pay "$10,000 in taxes."

As the minivan sped through Darien, the tension escalated. By now, Jennings alleges, Ammar was driving through blinking red lights and stop signs. Jennings says the cab doors were initially locked and he couldn't get out, though he says he later managed to get the door open and Ammar continued driving the cab with an open door.

He also claims Ammar was threatening. "If you don't pay me, I'm going to take you back to New York."

Jennings says he rooted around in his black briefcase for his cell phone and found a pen knife that he says he kept for opening the Christmas packages that had been arriving recently. He says he showed it to Ammar, and that Ammar grabbed it and then said, "you cut me."

Darien detectives would later discredit Jennings' claim, saying it would have been impossible for Ammar to grab the knife from Jennings through the narrow cab partition.

Ammar told police that after Jennings took out the pen knife, he began stabbing towards Ammar's neck and cut the taxi driver's hand, which later required six stitches. According to Ammar, Jennings cursed at him and then shouted "I'm going to kill you. You should go back to your country!"

The incident lasted only a few minutes. After the alleged stabbing, Ammar pulled over in front of the Darien Sports Shop, about a mile and half from Jennings' home.

Jennings bolted, racing home on foot, and later claimed in a statement to police that he was afraid the driver was going to come after him. Ammar yelled for help and dialed the police on his cell phone. By the time police arrived a few minutes later, Ammar's hand was "bleeding profusely," the police report said.

MYSTERY UNRAVELS

Sometime later, Jennings and his family apparently left for Florida for the holidays. At that point the police had no idea who had been in Ammar's cab. Ammar didn't have his name or address. And when police drove around Darien, Ammar couldn't remember where Jennings' house was. It was just too dark, he said. The roads were too narrow and unfamiliar. Darien detectives visited the G&G Deli and looked at video of Jennings buying food. But the image was murky and unclear.

The mystery began to unravel a few days after the incident, when a Darien newspaper ran a small item from a police report. Jennings had confided in a friend, telling him about the incident, he later told police. This person, who has not been identified, told Jennings when he saw the news story.

Jennings called a lawyer. On January 4, his lawyer called Darien police. Several conversations followed, and on February 29, Jennings turned himself in at Darien police headquarters. He posted $9,500 bail in cash.

(Reporting By Michelle Conlin; Editing by Scott Alwyn, Martin Howell)

• A Permanent Economic Emergency