The film begins with John (Brad Pitt) and Jane (Angelina Jolie) attending marriage counseling, where they reveal the struggles of their relationship. Having been married for "five or six" years, the couple reflects on the fact that they can't even remember the last time they were intimate. They recount their first encounter in Bogotá, Colombia, where both were secretly evading Colombian authorities. Their romance blossomed swiftly, ultimately leading to marriage. John fondly remembers that on the day they met, Jane "looked like Christmas morning" to him.
However, unbeknownst to each other, John and Jane are highly trained assassins, each working for rival firms and excelling in their respective techniques. Jane is meticulous and plan-oriented, whereas John has a more spontaneous approach. For years, they have been concealing their true professions from one another, allowing their seemingly ordinary marriage to grow increasingly mundane and stifling.
The tension escalates when they are both assigned the same target, Benjamin "The Tank" Danz (Adam Brody), leading to a chaotic confrontation. Mistaking each other for rivals, they find themselves in a series of failed assassination attempts characterized by a backdrop of betrayal. Their conflict culminates in an explosive confrontation within their home. After a long and intense struggle, guns are drawn, but as emotions surge, John lowers his weapon, and Jane cannot bring herself to shoot him either. In this moment of vulnerability, they realize their love prevails over discord.
Reunited, the couple is soon thrown back into peril as their employers decide to eliminate them. John's friend, Eddie (Vince Vaughn), refuses to accept a $400,000 bounty on their heads, which only increases the danger they face from a horde of assassins. As their house is destroyed in a ferocious attack, the Smiths hijack a neighbor’s minivan and take down several armored cars during a thrilling chase, all while bickering and sharing newfound personal revelations.
Determined to fight for their marriage, John and Jane concoct a plan to kidnap Danz from his high-security prison, believing it will appease their employers. During this encounter, Danz reveals a stunning twist; he was merely used as bait to instigate a deadly game between the spouses, hoping one would eliminate the other. Notably, he sports a t-shirt referencing "Fight Club," a nod to another iconic film featuring Brad Pitt.
Undeterred, John and Jane set aside their individual plans and unite as a formidable team, decisively confronting the onslaught of enemies in a high-stakes shootout inside a department store. In their final stand, they showcase an impressive synergy that solidifies their partnership.
The film concludes with the Smiths returning to their marriage counselor, now exuding genuine happiness as they share how their relationship has flourished and how deeply they cherish one another.
