In the dimly lit streets of Montmartre, a mysterious killer lurked, preying on innocent brunettes with a deadly blade. As the death toll rose to four, including a prostitute and a midwife, the pressure mounted on Chief Inspector Maigret to solve the case. Justice Minister Morel demanded swift action, and Maigret knew he had to act fast. With the help of policewoman Marthe Jusserard, he devised a risky plan to catch the murderer. Using Marthe as bait, they set a trap and waited for the killer to strike. When the killer attacked, Marthe narrowly escaped with her life, leaving behind crucial evidence that pointed to Marcel Moncin, a seemingly ordinary family man. Maigret wasted no time in arresting Moncin, but his troubles were far from over. As Moncin languished in custody, another body turned up, casting doubt on his guilt. Desperate for answers, Maigret delved into Moncin's family history, uncovering dark secrets that would lead him to the shocking truth behind the murders.