Chatelard, one of Viscount de Kerlec's guests, has died in mysterious conditions. The police initiates an investigation and sends detective-inspector Pauc to de Kerlec's manor. Pauc decides to mingle with the viscount's guests , who are all likely to have committed the murder. Among them, there is Jacques Mauclerc, a naval officer, and a seedy character named Bartoli, in fact a spy in search of secret documents. Pauc will end up untangling the web during a dramatic séance.