While in Brussels where he is being rewarded with the Order of Leopold, Maigret is asked for by a man named Xavier Marton who tells him that he suspects his wife Gisèle to want to murder him. Then the man disappears. The following evening a woman by the name of Gisèle Marton is waiting for him in the lounge when Maigret arrives in this hotel. She warns the French commissaire that he must not believe what her husband has told him as the man is paranoiac. Puzzled by this unusual situation, Maigret decides to investigate. At the Martons'luxurious house (another oddity considering what modest jobs the couple have) he meets Jany, Gisèle's sister, who lets him know that he shouldn't believe all her sister says...