A little old lady, Léontine Antoine, tries to see Maigret at the Quai des Orfèvres. Lapointe interviews her and they learn that she believes someone has been in her apartment, as things have been moved around. She approaches Maigret in the street and makes him promise to come, but before he has a chance, he learns she has been murdered in her apartment. Apparently she'd returned while the unknown intruder was there. If only Maigret can learn what the mysterious intruder had been searching for, but she apparently had nothing of value in the house. The only strange item is a piece of paper with revolver grease found in her bedside table drawer. Her mannish masseuse niece, Angèle Louette, lives nearby, and her boyfriend turns out to be a petty criminal, Le Grand Marcel, but soon after Maigret confronts him in her apartment, he leaves for Toulon; apparently they had a quarrel and have split up.
Maigret calls his old friend Marella in Toulon to watch Marcel, and when he hears he's visited retired crime lord Pepito Giovanni, heads for the scene. Maigret and Marella go to Giovanni's, and shortly after they see him head out to sea briefly in his launch. He has thrown the revolver into the sea. Maigret returns to Paris where Marella calls him the next day to report that Le Grand Marcel was found shot to death. When Maigret confronts Angèle Louette with this news, she reveals that Marcel had wanted her aunt's late husband's invention, a silencer-revolver, thinking he could sell it. He'd killed her when she returned while he was still there. Since it was an unpremeditated crime, she cannot be held as an accessory, and Maigret decides to let her go free.
This report prepared by Dana Samson