The film kicks off with Martin Q Blank (John Cusack), a hired assassin, meticulously prepping a high-powered rifle while on a call with his assistant, Marcella (Joan Cusack). As he hunts down a bike messenger in the bustling streets of Los Angeles, Marcella reads an invitation to Martin's ten-year high school reunion in Grosse Pointe, his hometown near Detroit. In the midst of the chaos, Martin dispatches the messenger just as a target emerges from a hotel, igniting a frenzied shootout. Amidst the confusion, he spots his rival, Grocer (Dan Aykroyd), another assassin who is establishing a coalition of killers, but Martin, feeling disillusioned and annoyed, prefers to work solo.
Struggling with his profession and facing increased competition, Martin experiences an existential crisis after a botched assassination attempt. Marcella informs him that to salvage the failed contract, he must head to Grosse Pointe, allowing him to attend his reunion and complete the job over a weekend. His therapist, Alan ([Alan Arkin]), nudges him towards attending, but tension looms as Martin wrestles with memories of his high school sweetheart, Debi Newberry (Minnie Driver), whom he left on prom night a decade earlier.
When Martin finally arrives in Grosse Pointe, he faces the painful remnants of his past: his childhood home is replaced by a convenience store, his mother suffers from severe dementia, and his father has passed away, leading him to pay an unconventional tribute by leaving an empty whiskey bottle on the grave. His reunion with Debi, now a radio DJ, is awkward and tense, filled with unresolved feelings of guilt as she frequently reminds him of his abandonment.
Reconnecting with old friends brings little comfort, as Martin finds himself out of sync with their mundane lives. When he openly declares his occupation as an assassin, he’s met with laughter, unaware that rival hitmen, including Grocer and Felix LaPubelle (Benny Urquidez), are hunting him down. Meanwhile, two awkward NSA agents are on his tail, waiting for an opportunity to intervene.
As events unfold, Martin's past decisions weigh heavily on him. A confrontation with LaPubelle at the UltiMart escalates into chaos. Over breakfast with Grocer, Martin again dismisses his offer to join forces, even as romantic sparks reignite with Debi during the reunion. In a moment of clarity, Martin gazes into a child’s innocent face, prompting him to reconsider his life choices. An impulsive encounter with Debi leads them to a health office where they share a passionate moment.
However, the peace is shattered when LaPubelle finds Martin, triggering a fierce battle that culminates in Martin defending himself with a pen. Debi's horrified reaction sends her fleeing, prompting Martin to enlist Paul for help in disposing of LaPubelle's body. Later, he confides in Debi about his secretive, morally ambiguous past, which only drives her further away.
Faced with an unexpected realization that his target is Debi's father, Bart Newberry (Mitchell Ryan), he chooses to protect Bart from Grocer, valuing his newfound respect for life over his deadly contract. In the chaos of Grocer's attack on the Newberry home, Martin battles multiple adversaries while hiding Debi and her father to keep them safe.
In this climactic confrontation, Martin reveals the real reason he left Debi long ago. As he eliminates threats one by one, he ultimately proposes marriage, earning Bart's approval, yet leaves Debi speechless from the tumultuous events. With a whirlwind of emotions, Martin and Debi escape Grosse Pointe together, hinting at a new beginning.
