After telling Maigret she overheard a plot to kill 'the countess' club singer Arlette is strangled and soon afterwards the body of an elderly, reclusive countess is also discovered. Maigret believes a third person was present when Arlette was killed and is anxious to trace a man called Oscar, whose name Arlette cried out in her sleep. Meanwhile young rent boy Philippe, who shared the countess's drug addiction, n survives an attempt on his life but is too scared to help the police. Maigret finds out that both the dead women once lived at a Nice hotel, where the countess's husband died in odd circumstances and where Oscar also worked. This leads him to track down Oscar and to the closure of his case.