Over a five month period in 1955 four women are stabbed to death in montmartre after dark, a prostitute and a midwife among them - women with nothing in common beyond being brunette. justice minister morel leans on chief inspector maigret to catch the murderer and maigret sets a trap, using policewoman marthe jusserard as a decoy. she survives an attack, sartorial evidence leading to married mother's boy marcel moncin, whom maigret arrests. however whilst moncin is in custody there is a further murder and maigret looks to moncin's family to help solve the murders.