Based on the famous Belgian graphic novel XIII (but not otherwise related to Ubisoft's eponymous 2003 first-person shooter XIII based on the same source material), XIII: Lost Identity is a hidden-object game in which players take the role of the amnesiac man identified only through the Roman numeral for 13 tattooed on his chest. After washing up ashore somewhere in Northern America, barely alive, "XIII" is taken in by an elderly couple and starts the search for his true identity and past, which will lead him to discover a great conspiracy that reaches into the highest levels of the U.S. government.
Sticking closely to the storyline of the original graphic novel series, but omitting numerous passages and books, the hidden-object scenes are interspersed with jigsaws and other tile-based puzzles, short shooting gallery action sequences, and numerous dialogues with major characters. There are no dialogue choices and the story is linear. Many of the locations and characters are presented using touched-up and recolored versions of the original artwork from the graphic novels.
The game covers the plot of the official comic series up to the conclusion of book 8. While it omits several scenes and subplots, and completely skips books 6 and 7, it generally sticks more closely to the original story than the XIII first-person shooter.