The President of the United States, William Sheridan, is found murdered. An unknown man is discovered on a beach, shot in the temple and bearing the number XIII tattooed on his left collarbone. Suffering from amnesia, he is identified as President Sheridan's killer. As powerful civilian and military figures take a keen interest in him, he realizes he is at the center of a dangerous plot. Hunted and manipulated, he must set out in search of his identity and his past. But above all, he must uncover the truth about what is going on... while escaping the killers on his trail and the mysterious conspiracy of the XX.