Henry Brogan (Will Smith) is an elite hitman, an absolute professional who always does the job without fail. However, on his last job, information he shouldn't have heard has been leaked to him, so his heavy-hearted employer decides to have him eliminated.
But who to send to the man who is the best in the business? Ideally, Henry's double, a little younger, more resilient and determined. At Gemini, a company run by technocrat Clay Veris (Clive Owen), a secret project has been running for years that offers just that possibility. For the first time, Henry fears for his life. On his heels is an equal opponent who anticipates his every move and strikes back with a slightly stronger counterpunch.
Accompanied by undercover agent Danny (Mary Elizabeth Winstead), he flees frantically across continents before realising that he must face his pursuer if he is to have any chance of survival. Against the grim backdrop of the Budapest catacombs, he finally manages to corner him, but when he looks him in the eye, he suddenly has far more questions than answers. He's up against his thirty-years-younger self, and he still wants to kill him...