A severely injured amnesiac man is found with no memory of his identity or his past. His only clue is the number XIII tattooed on his collarbone. Soon hunted by killers and watched by the authorities, he discovers that he may be connected to the assassination of the President of the United States and to a vast conspiracy involving high-ranking civilian and military officials. As he flees and investigates, XIII assumes several identities and tries to reconstruct his history while confronting those who seek to manipulate or eliminate him. His personal quest gradually becomes a political thriller in which memory, espionage, and state secrets are deeply intertwined.