The murder investigation of a diamond dealer from Antwerp seems to point at one man - Carl Andersen, a Danish citizen living in the outskirts of Paris. But, despite all the evidence, Maigret lets him go, much to the annoyance of old friend and colleague Inspector Grandjean. So why was the body of a diamond merchant found at his isolated mansion? Why is his sister always shut away in her room? And why does everyone at Three Widows Crossroads have something to hide?