On August 22, 1972, first-time crook Sonny Wortzik, his friend Salvatore “Sal” Naturale, and Stevie attempt to rob the First Brooklyn Savings Bank. The plan immediately goes awry when Stevie loses his nerve and flees, and Sonny discovers they have arrived after the daily cash pickup, finding only $1,100 in cash.
Sonny takes the bank’s traveler’s cheques and burns the register in a trash can, but the smoke raises suspicion outside, and the building is surrounded by police. The two panicked robbers take the bank employees hostage.
Police Detective Sergeant Eugene Moretti calls the bank and Sonny bluffs that he is prepared to kill the hostages. Sal assures Sonny that he is ready to kill if necessary. A security guard has an asthma attack and Sonny releases him as a display of good faith. Moretti convinces Sonny to step outside. Using the head teller as a shield, Sonny begins a dialogue with Moretti that culminates in his shouting “Attica! Attica!” to invoke the recent Attica Prison riot. The crowd begins cheering for Sonny.
Sonny demands a vehicle to drive himself and Sal to the airport so they can board a jet. He also demands for pizzas to be brought for the hostages, and for his wife to be brought to the bank. Sonny’s partner, Leon Shermer, arrives and reveals that the robbery was intended to pay for her sex reassignment surgery, as she is a trans woman. She divulges that Sonny has children with his estranged wife, Angie.
As night sets in, the bank’s lights are shut off as FBI Agent Sheldon takes command of the scene. He refuses to give Sonny any more favors, but when the bank manager Mulvaney goes into diabetic shock, Sheldon lets a doctor inside. Sheldon convinces Leon to talk to Sonny on the phone; she reveals that she attempted suicide to escape the abusive Sonny, and was hospitalized at Bellevue Hospital when police found her. Leon turns down Sonny’s offer to join him and Sal in their escape. Sonny tells police that Leon had nothing to do with the robbery.
Sonny agrees to let Mulvaney leave, but he refuses to leave his employees. The FBI calls Sonny out of the bank to talk to his mother, who unsuccessfully tries to persuade him to give himself up. Back inside, Sonny writes out his will, leaving money from his life insurance to Leon for her surgery and to Angie.
When the requested limousine arrives, Sonny checks for hidden weapons or booby traps, and selects Agent Murphy to drive him, Sal, and the remaining hostages to Kennedy Airport. Sonny sits in the front beside Murphy with Sal behind. Murphy repeatedly asks Sal to point his gun at the roof so Sal won’t accidentally shoot him.
As they wait on the airport tarmac for the plane to taxi into position, Sal releases another hostage, who gives him her rosary beads for his first plane trip. Murphy again reminds Sal to aim his gun away. Sal does, and Sheldon seizes Sonny’s weapon, allowing Murphy to pull a revolver hidden in his armrest and shoot Sal in the head. Sonny is immediately arrested, and the hostages are freed.
The film ends as Sonny watches Sal’s body being taken from the car on a stretcher. Subtitles reveal that Sonny was sentenced to 20 years in prison, Angie and her children subsisted on welfare, and Leon, who changed her name to Elizabeth, was able to have the surgery.