A woman is found murdered near a canal lock, in a remote and muddy area connected to barge traffic. Inspector Maigret investigates the case among canal workers and the crew of the barge La Providence. As he questions the people living and working on the canals, he uncovers hidden tensions, secrets, and relationships that explain the crime.
The novel focuses less on action and more on atmosphere and psychology, showing how Maigret slowly pieces together the truth behind a quiet but disturbing murder.