Maigret investigates the circumstances when a homeless tramp is recovered from the Seine, after being attacked and badly wounded.

His wife, estranged but not divorced, is persuaded to visit him in hospital, but displays no affection or interest in a reconciliation.

The tramp, identified as François Keller, was rescued by Jef van Houtte, a Belgian barge owner, and whilst in hospital, refuses to talk.

Under intense interrogation, van Houtte eventually confesses that many years ago he was responsible for the death by drowning of his father-in-law and that Keller was a witness.

But Keller still won't say anything, and Maigret is forced to release the Belgian for lack of evidence.