Cy Vance Jr. grew up among the elite of Washington after the family moved to the capital from the Upper East Side in 1960. His father took him fishing at Camp David. He spent the night at the White House and met President Lyndon B. Johnson when he was 12. He followed his father to Yale, where he studied American history. Determined not to become a lawyer, he peddled oil-marketing services in West Africa. He wasn’t very good at it, and after five years he reconciled himself to his father’s profession, enrolling at the Georgetown University Law Center. He graduated in 1982, shortly before his 28th birthday. Robert M. Morgenthau liked to say he had one rule — “never do a politician a favor''— but he hired his share of celebrity lawyers’ sons, and Vance landed a coveted assistant D.A. position. He was assigned to Trial Bureau 80, where the halls were piled with cardboard boxes and the blue carpet underfoot was so memorably gross that Vance was given a framed swatch of it as a keepsake when it was finally replaced. “That time was the wild west,” recalled Jeffrey Schlanger, Vance’s chief of staff, who got to be friends with him when they worked together in the Rackets Bureau. “The crack epidemic was going. Arraignments had a feeling of controlled chaos. I remember one mentally ill defendant pulling feces out of his pants. Every day was a scramble. We were learning things they didn’t teach in law school.”

Trials were what appealed to Vance — the strategies, the characters, the drama of verdicts, the satisfaction of knowing his work mattered. He handled cases from murder to art theft to animal cruelty and made friends with people you don’t normally see at Yale reunions. He loved getting up in the middle of the night to inspect crime scenes with detectives from the robbery squad. “We focused on pattern robberies,” he recalled, “like the guys who specialized in shotgun stickups of Häagen-Dazs stores.”

After six years, Vance was ready to get out from under the shadow of his father’s fame. Against the advice of his dad, who said he was “waving the white flag” on his career, he found a job as an associate at Culp Dwyer Guterson & Grader in Seattle, where he moved with his wife, Peggy McDonnell, whom he’d married in 1984. He proved adept at white-collar criminal defense work, eventually made partner and then seven years later left to start his own firm. “He was the criminal lawyer in Seattle,” recalled Robert Sulkin, a founding member of McNaul Ebel Nawrot Helgren & Vance. “When you got into trouble, you called Cy Vance.”

Vance handled most of the firm’s criminal work, taking cases that political opponents would later try to use against him, like his defense of Joseph Meling, an insurance salesman convicted of killing two people in an attempt to cover his tracks after trying to poison his wife with cyanide-laced Sudafed. Years at the defense table underlined for Vance some of the prosecutor’s powers. “The philosophy I have about law enforcement — enhancing public safety while enhancing fairness — didn’t come from my father, and it didn’t come from reading or professors in law school,” Vance said. “It came from years of practical experience as a prosecutor and a defense attorney.”

On trips back East, Vance would call on Morgenthau. In January 2002, his father died after a long decline. Two years later, with their children, Simon and Clare, on the brink of high school, and Vance’s mother and his sister Amy debilitated by illness, Peggy thought it was time to come home. With the help of Morgenthau and Eliot Spitzer, then the New York State attorney general, whom Vance met in the Rackets Bureau, Vance landed a job in New York as a partner at a boutique white-collar firm, Morvillo Abramowitz. He had been back in the city a year or so when he confided to his wife that he was thinking of running for Manhattan district attorney if Morgenthau retired. His political résumé at the time consisted of passing out fliers for Lyndon Johnson and a couple of days of advance work for Gary Hart’s unsuccessful presidential bid in 1984.

So numerous were the stumbles in Vance’s first term that for a while it looked as if he might not have the luxury of a second. At one point the Data D.A. had a far more formidable reputation on the Facebook pages of East Harlem gangs than he did in the New York press. The New York Post labeled him, “Soft Cy,” “Manhattan’s hapless district attorney” who learned to fight crime in the “espresso bars of Seattle.”

“Cy’s first 18 months in office were so bruising that having no opposition for re-election was something I never expected even a year ago,” says Linda Fairstein, a former Manhattan sex-crimes prosecutor and Vance adviser. The nadir of his rookie woes came in August 2011, when the sex-crimes prosecution of the French politician Dominique Strauss-Kahn collapsed. It’s hard to imagine Vance will ever again find himself in a maelstrom like the drama of Strauss-Kahn and the Sofitel housekeeper Nafissatou Diallo: 19 New York Post cover stories; writhing news-media scrums outside the Criminal Courts Building; armchair prosecutors dissecting how the green D.A. and his mismanaged minions were in over their heads. Kenneth Thompson, who at the time was the attorney for Diallo and now is the district attorney in Brooklyn, tore into Vance in front of TV cameras: “If the Manhattan district attorney, who is elected to protect our mothers, our daughters, our sisters, our wives and our loved ones, is not going to stand up for them when they’re raped or sexually assaulted, who will?” (Many months later, when Thompson was preparing to run for public office himself, Vance says Thompson privately apologized. Thompson says that he did call to say he shouldn’t have said Vance was afraid to try the case, but that that didn’t constitute an apology.)