Lucerne, the first day of carnival, nicknamed "Dirty Thursday". Early in the morning, Franz Schäublin, Head of Lucerne's Building Commission and active guild member, is found stabbed amidst the hustle and bustle of the carnival. Witnesses report seeing a man costumed as Death running from the crime scene. The murder victim had run up a high hotel bill and was carrying a large amount of cash. Initial police investigations reveal that Schäublin appears to have led a double life. Searching for the perpetrator, Reto Flückiger and Liz Ritschard plunge into the pandemonium of their carnival-crazed city. Striving hard to unmask and reveal the deadly reveler, they finally realize that the killer has made fools of them.