A young man named Wesley Gibson (James McAvoy) works at a dead-end job with an overbearing boss. He takes depressant when he feels stressed out. His live-in girlfriend is sleeping with his best friend. He speaks of how his father left when he was just one week old. He wonders if maybe when he was born his father looked into his eyes and saw a failure.
Elsewhere, a man called "Mr. X" (David O'Hara) meets with a ballistics expert to find out who made a particular bullet for a "competitor". She observes that the bullet is "clean", i.e., not traceable to a particular gun. (As becomes clear later, this is because it is the last stage of a multi-stage bullet.) Suddenly, a sniper shoots the ballistics expert in the head from a nearby building. Mr. X leaps through the window and shoots his opponents in mid-flight, killing them. He lands on the building and begins talking to a man on a cell phone, unaware that he is standing on a marked spot. He notices it as the man, named Cross fires a multi-stage bullet from across town, killing Mr. X by going through the back of his head and out through his forehead (the flight of the bullet is shown in slow-motion, backward).
Wesley Gibson (James McAvoy) é um jovem de 25 anos de idade que não vê muito sentido na vida após o misterioso assassinato do pai. Tudo muda quando Wes conhece Fox (Angelina Jolie), uma mulher enigmática e sedutora que o contrata para uma sociedade secreta chamada de Fraternidade. O objetivo de Fox é treinar Wes para que ele se torne um assassino da Fraterninade, mas também se vingue da morte do pai. Aos poucos, no entanto, o rapaz vai descobrindo que o perigo está mais perto do que os olhos podem ver.