The movie opens with a caption declaring that what follows is largely inspired by real events.

We’re introduced to Gary Johnson (Glen Powell), a calm, intelligent philosophy professor giving a lecture about Nietzsche’s concept of self-actualization. One student mocks his outdated car, a quiet jab that hits home. Gary’s voiceover begins, revealing his simple, solitary life shared only with his two cats, Id and Ego. Outside his university duties, Gary moonlights with the New Orleans Police Department as part of a sting operation to expose people seeking contract killings.

The department’s usual undercover man, Jasper (Austin Amelio), is temporarily benched after assaulting teenagers. With few other options, officers Claudette (Retta) and Phil (Sanjay Rao) push Gary to step into the dangerous role of pretending to be a killer-for-hire. Gary is hesitant and worried about his safety, but ultimately agrees.

Disguised as “Billy,” Gary meets with his first client, Craig (Mike Markoff), and surprisingly manages to portray a deranged assassin with chilling believability. Once Craig offers payment and details for a hit, police swoop in and arrest him. Gary’s convincing performance earns him praise, and he continues the role for future cases.

Each new client demands a different version of a hitman, and Gary proves a chameleon — slipping into unique personas, often eccentric or terrifying, depending on the target audience. He develops a knack for it, even testifying in court to ensure these individuals are held accountable. His efforts boost his image among his students, who now see him as more confident and charismatic.

Things take a turn when Gary receives a case file on Madison Figueroa Masters (Adria Arjona). Before the meeting, he investigates her online and notices her past is murky before her marriage to Ray (Evan Holtzman). As “Ron,” Gary meets Madison at a diner. She confides in him, expressing desperation over her toxic marriage. But Gary finds himself enamored with her and urges her to keep the money and escape instead of commissioning a murder. Against police protocol, he lets her walk.

Claudette and Phil disapprove, warning Gary about crossing lines. Meanwhile, Jasper returns and quickly realizes he’s been replaced. He bristles at the department’s preference for Gary, and bitterness festers.

Madison reaches out to “Ron” and invites him to a pet adoption event. Though Gary’s a cat person, he goes and enjoys himself, even winning over the dogs and children. His chemistry with Madison grows, and eventually, they sleep together and begin a secret relationship. Gary hides the affair from his police colleagues.

While out on a date, Madison and Gary are spotted by Ray and a friend. Ray reacts with rage and attempts to hit Madison, prompting Gary to pull a gun and intimidate him. Later, Gary sees Jasper lurking nearby. Jasper greets them casually, not revealing their shared past to Madison, but it rattles Gary.

Gary receives another hit request — this time from someone calling himself “Mike.” It turns out to be Ray, trying to have Madison and her new lover killed. Gary drops the act, reveals his true identity to Ray, and scares him off.

Later, Ray turns up dead. Gary is informed at the station that it looks like a drug deal gone bad. He rushes to Madison’s place, only to hear her confess to shooting Ray after learning of his murder plot. Gary then reveals that he’s not a hitman but a police decoy — a confession that devastates Madison. She throws him out.

Police soon suspect Madison, especially when it’s revealed she was the sole beneficiary of a $1 million life insurance policy Ray recently updated. They want Gary to wear a wire and trap her into confessing. Knowing she now distrusts him, Gary covertly alerts her that the cops are listening during their recorded conversation. They put on a fake, benign exchange, fooling law enforcement.

Later, Gary arrives at Madison’s home to find Jasper inside. Jasper plans to blackmail the couple for a share of the insurance payout, having figured out both Gary’s identity and Madison’s secret. Madison serves Jasper a beer laced with sedatives, and as he starts to lose consciousness, Gary calmly suffocates him with a plastic bag. They agree to make his death look like a suicide — an overdose, easily explained due to his reckless past. In the aftermath, the two admit they love each other.

Years pass. Gary now lectures to a packed classroom, evidence of his growing popularity. He’s married to Madison, and they’ve built a life with two kids and two dogs. One day, their daughter innocently asks how her parents met. Smiling, Gary and Madison concoct a sweet, sanitized story — a casual meet-cute at a café where they helped each other grow.

The film ends with a tribute to the real Gary Johnson, who passed away in 2022. It notes his achievements as a university professor, war veteran, Buddhist, and animal lover — and that, despite his undercover role, he never actually killed anyone.