XIII is a cel-shaded first-person shooter based on the popular Belgian cult comic created by Jean Van Hamme and illustrated by William Vance. The game is loosely based on the first five comics. The player unravels clues, trying to solve a conspiracy set in an environment that breathes a comic book ambiance. Footsteps and shots are visualized in text and actions: for example, headshots are shown in a series of still images. Aside from that, the game has all the typical FPS elements: both stealth and action, more than fifteen weapons (shotguns, crossbows, rifles, ...), interaction with environmental objects and plenty of enemies in levels spread all over the world. During the game, the player can learn a number of skills such as silent walking, lockpicking and dual weapons handling.

The President of the United States of America has been assassinated and you're the world's prime suspect. The FBI, the CIA, and a gang of murderous killers are trying to hunt you down. Stricken with amnesia you remember nothing, not even who you are. You're on your own and there is no one you can trust. All you have is a safe deposit key, a mysterious tattoo, and a gun. Clear your name, solve the mystery, and catch the true assassin before he strikes again.