The Thirteenth Floor begins with the murder of Hannon Fuller (Armin Mueller-Stahl), he is murdered before he can tell his colleague about a big discovery his has made. His colleague, Douglas Hall (Craig Bierko) is the main suspect with evidence clearly stacking against him, however he proclaims his innocence and soon finds out that Fuller has left clues to his discovery and death in a virtual reality program. The program is based on the 1930s and Hall must delve into that reality to find out who killed Fuller and why. Hall's trips into the virtual world will lead him to not only many discoveries about Fuller's death but also about his own life.