A man collapses in Beethovenstrasse. His murderer flees. The dead man, a private detective from New York, was on the trail of an international blackmail ring. Supported by customs investigator Kressin, Sandy, the dead man's partner, takes over the case. He manages to sneak into the blackmail ring. But the turbulence of the Cologne carnival makes the case more and more confusing, inscrutable and ultimately ends in a dark, bloody nightmare.