In the film, a small group of Irish-American gangsters operating in the section of New York City, west of Times Square, known as Hell's Kitchen. When their territory is threatened by gentrification, the boss, Frankie Flannery (Ed Harris) tries to arrange an alliance with the Italian Mafia, their rivals.
Frankie welcomes back Terry Noonan (Sean Penn) to the neighborhood and into his organization after a long absence. Unknown to the gang, however, during his time away, Terry has become a police officer in Boston. He's been brought back to New York specifically to go undercover in his old neighborhood and bring down the Irish gangsters before they strike a deal with the Italian-Americans.