Maigret has a hard task to complete. He must visit a man he arrested in prison with the news that his reprieve has been refused and he will be executed at dawn. But the condemned man tells Maigret a surprising story – of seeing a body dumped in the Canal Saint-Martin six years before and of blackmailing the murderer. This leads Maigret to the ‘Guinguette’, a bar by the River Seine, where he is drawn into the company of its regular customers. Is the murderer of Lenoir’s story among them? When another murder is committed, Maigret must untangle a disturbing web of secrets …