In the Boston area, a gang of bank robbers has been operating by holding hostage the families of bank managers, thereby forcing them to cooperate with the thefts. Supplying guns to the gang is Eddie Coyle, an aging, low-level underworld hood who is weary of his illegal activities and longs for a placid life. One evening, Eddie meets for the first time with Jackie Brown, an arrogant young man whose name has been provided to Eddie as a gun runner. Eddie, both pragmatic and cynical, explains to Jackie that if he ever crosses the men with whom he deals, even if by mistake, he will be severely punished, although it will be business and not personal. While Eddie and Jackie are bargaining about the merchandise, which Jackie claims cannot be traced, the younger man lets slip that he is going to be selling machine guns to someone else. Eddie then goes to see Dillon, a bartender and sometime hit man who often acts as a go-between in the underworld. Eddie complains to Dillon about his current legal woes, which resulted from smuggling stolen liquor for Dillon. Eddie was arrested in New Hampshire and, because he refused to “rat” on Dillon, was found guilty on a federal charge and is about to be sentenced to several years in prison. Eddie agonizes about returning to prison, as he does not want his wife and three children to have to go on welfare, but Dillon dismisses his troubles, stating that Eddie wanted a “job” and Dillon gave it to him. Later, Dillon surreptitiously meets with Dave Foley, an undercover U.S. Treasury agent to whom Dillon supplies information about organized crime activities. Dillon intimates that something big is brewing, as he has been relaying numerous messages for various people, including Eddie and Jimmy Scalise, the leader of the bank robbers. At home, Eddie is distraught when his wife Sheila casually mentions that her mother will look after their children so that Sheila can work while Eddie is in prison. Eddie insists that he will rectify the situation then goes to meet Foley, for whom he is an occasional and reluctant informant. Eddie pleads with Foley to call the U.S. district attorney in New Hampshire and vouch for him, but Foley maintains that he can make the call only if Eddie is willing to help “uncle” by giving him good information. Knowing that it would be dangerous to inform on the volatile Scalise, Eddie offers Foley the name of someone selling machine guns. Meanwhile, Jackie meets with customers Andrea and Pete, violent youths who want the machine guns to rob a bank, and agrees to supply them for a large sum. The following day, Eddie meets Jackie at a bowling alley and demands that he fulfill the rest of their agreement by getting ten more pistols by the next evening. Although Eddie does need the weapons to give to Artie Van, Scalise’s right-hand man, he is also pumping Jackie for information about his other dealings without the young man realizing it. Eddie bitterly rants about how hard he has worked while others have hit the “big time” and are now relaxing in Florida. That night, Jackie goes to Rhode Island, where he accepts a load of stolen machine guns. In the morning, Scalise and his gang rob another bank, although when an employee sets off the alarm, one of the gunmen shoots him in anger, and the manager, whose wife is being held hostage, is beaten into unconsciousness. When Artie meets with Eddie later, Eddie worries that the gang, and by extension himself, will become the targets of an FBI search, but Artie reassures him that because the bank was not federally insured, only local police will be involved. Artie also reprimands Eddie for attempting the liquor job with Dillon, stating that the barkeeper is an excellent hit man but incompetent with other affairs. Boasting that their next job will be such a big one that they will be able to retire afterward, Artie then requests more guns from Eddie. Soon after, Dillon again meets with Foley, to whom he confesses that he is worried about retribution if it becomes known that he is a “snitch.” Foley asserts that he is aware of Dillon’s position and that “uncle” appreciates his cooperation. That afternoon, Jackie turns over the pistols to Eddie, then goes to the parking lot where he is to meet Pete and Andrea. Having been alerted by Eddie, Foley and his men are lying in wait, but when the suspicious Jackie sends the buyers away before completing the transaction, the agents are forced to grab only Jackie, thereby making the arrest less important. That night, Foley meets Eddie, who is crestfallen to learn that the arrest was not enough to persuade the New Hampshire district attorney to drop his case. The calculating Foley then tells him that only by offering key information on a more regular basis can he hope to please “uncle” enough. Disgusted by the idea of becoming a “permanent fink,” Eddie declares that he should have known better than to trust a cop. That night, Eddie brings Scalise groceries and guns and carefully pumps him for information about their next robbery, which Scalise, like Artie, boasts will be a big one. The next day, Scalise, Artie and their men talk with Dillon, who suggests that Eddie is “swapping them” for release from the New Hampshire conviction. Artie maintains that Eddie is a “standup guy,” while Scalise is certain that Eddie does not have enough details about their operation to be a danger. Soon after, Scalise and the gang sneak into a suburban home to abduct another bank manager, but Foley and his agents are waiting and arrest them. Unaware of the arrest, Eddie meets with Foley and, desperate to avoid prison, offers him information about Scalise, but Foley coldly tells him that he is too late and leaves. Meanwhile, Dillon meets with a representative of “The Man,” the head of their organization, who has put out a contract on Eddie for supposedly informing on Scalise. Dillon accepts the job and persuades an unsuspecting Eddie to attend a hockey game with him that evening. At the game, they are joined by a young hoodlum whom Dillon states is his wife’s nephew, and Dillon succeeds in getting Eddie drunk. The young man then drives them back to the bowling alley where Eddie left his car, and as they drive through a tunnel, Dillon shoots and kills Eddie. After dumping Eddie’s body in his car, Dillon departs to dispose of the gun. Soon after, Dillon meets again with Foley, who acknowledges his helpfulness in supplying the information that led to Scalise’s arrest. When Dillon rambles about other matters, Foley states that he is still grateful even though Dillon is unwilling to discuss Eddie’s death. Declaring that they are friends, Foley claims that he has never yet asked a friend to do something he could not.