Hitman Martin Blank finds himself depressed and disillusioned with his work. Grocer, his chief rival, is attempting to “unionize” the hitman business, ostensibly to avoid situations in which members of their profession would find themselves pitted against each other. Martin refuses to join, putting the two at odds. Following a botched contract, Martin accepts an invitation to his ten-year high school reunion in his hometown of Grosse Pointe, Michigan. He is persuaded into going by both his reluctant therapist, Dr. Oatman, and his secretary Marcella, who books him a contract in Michigan that coincides with the reunion, ostensibly to make amends with the client whose contract was botched.
In Grosse Pointe, Martin reconnects with his childhood friend Paul and his high school sweetheart Debi Newberry, now a radio DJ, whom Martin had abandoned on prom night to enlist in the Army. He freely admits to his former classmates that he is a professional hitman, but everyone assumes he is joking. He also visits his mentally ill mother in a retirement home and his father’s grave.
While he reacquaints himself with the town and his old friends, Martin is stalked by Felix LaPoubelle, another hitman, who attempts to kill Martin in a convenience store built on the site of his childhood home. He is also followed by two National Security Agency agents who were tipped off to Martin’s contract by Grocer. Despite these dangers, Martin remains distracted by his desire to reconcile with Debi and repeatedly procrastinates opening the dossier on his target.
Debi is conflicted about her feelings for Martin, but he manages to persuade her to attend the reunion with him.
At the reunion, Martin and Debi mingle with their former classmates and begin to fall in love all over again. Later, while exploring the halls alone, Martin is ambushed by LaPoubelle, whom he kills in self defense. Debi stumbles upon the scene as Martin is stooped over LaPoubelle’s corpse, and flees from the reunion in shock and horror. Paul arrives moments later and helps Martin dispose of LaPoubelle’s body in the school furnace.
Debi later confronts Martin in his hotel room, still reeling from the revelation that he was telling the truth about his profession. He reveals that when he joined the army, his psychological profile indicated a certain degree of “moral flexibility” that prompted the Central Intelligence Agency to recruit him as an assassin, after which he decided to freelance. Martin attempts to assuage Debi by assuring her that he only accepts contracts on corrupt individuals saying, “If I show up at your door, chances are you’ve done something to put me there.” His efforts to rationalize his work further anger Debi and she rejects his attempts at reconciliation and walks out.
Debi’s rejection of him gives Martin an emotional breakthrough, and he abruptly decides to retire from being a contract killer. He fires Oatman over the phone, lays off Marcella and orders her to incinerate their office, and finally opens the dossier detailing the contract that brought him to Grosse Pointe. He is surprised to find that the target is Debi’s father, Bart, who is scheduled to testify against Martin’s benefactor.
Accompanied by several henchmen, Grocer decides to kill Bart himself to impress Martin’s client. Martin abandons the contract and rescues Bart, driving him to the Newberry house and holing up inside. Grocer, his cohorts, and the NSA agents descend upon the house. During the siege, Martin finally admits to Debi that he left her on prom night to protect her from his homicidal urges, which were due to his troubled upbringing. Martin methodically picks off Grocer’s henchmen, and the NSA agents are gunned down by both Grocer and Martin. Martin then kills Grocer by smashing a television over his head. Injured and winded, Martin proposes marriage to Debi, who is too stunned and despondent by the killing spree to respond. Debi’s father quips, “You have my blessing.”
Debi and Martin then leave Grosse Pointe together, with Martin presumably feeling more psychologically well-adjusted.