The series begins with a man awakening to find himself washed ashore in the eastern United States and suffering from amnesia. The only links to his past are a tattoo of the Roman numerals "XIII" on his collarbone and a photo of himself with a woman, who is identified as Kim Rowland, widow of U.S. Army captain Steve Rowland. Volumes 1 through 5 deal with "XIII" searching for his identity and past. He finds himself hunted by a contract killer, the "Mongoose", who works for a mysterious organization known as XX, which aims to mount a coup d'état against the U.S. government. XIII is rescued from XX's assassins by the Federal Bureau of Investigation's Colonel Amos, who confronts XIII with video evidence that shows XIII assassinating the President.