Maigret and the Saturday Caller (Inspector Maigret #59)

Maigret has a visitor who admits his intentions to commit murder but when he goes missing Maigret worries that he himself has become the victim

Inspector Maigret is followed home one evening by a man who reveals his intention to kill his wife and her lover. Maigret intervenes and speaks to the man daily but when the calls suddenly stop Maigret finds a murder on his hands.