Anthropologist Tobias Schmidt-Eberbach is about to get married. However, a find of a prehistoric skull on his wedding day messes up his plans. So does hitchhiker Uschi Mueller who he picks up merely by accident. It does not help that the police thinks that Tobias is a serial killer and Uschi his next victim, and neither that the real killer is still on the loose…

The inventor Sir Claude Amery wants to give the thief of the formula for his latest invention the chance to return it in the dark without being recognized. He gathers everyone in the house in the library and has the lights switched off for a short time. When the light comes back on, Amery is dead. A case for the Belgian master detective Hercule Poirot.