4 ideas
Pietr the Latvian, head of an international swindling ring, arrives in Paris on the Étoile du Nord, and a dead man resembling him is found in the train's lavatory. Maigret learns that Pietr had a twin, Hans, long overshadowed by him.
Maigret does not solve the case by deduction. He plants his heavy, unhurried presence next to the suspect: tailing him openly, drinking in the same bars, waiting in the same hotel lobby. The pressure of being watched by someone who does not leave makes the suspect's composure crack, and the cracks reveal more than clues would.
A man can switch clothes, names and social class, moving from a luxury guest at the Majestic to a shabby drunk in the immigrant quarter or on the coast. What he cannot switch is his ingrained habits of gesture, posture and nerve. Read the small involuntary behaviors that survive the change of costume, not the costume itself.
The decisive step is not proving what happened but grasping how the man lives and what old grievance drives him, here a lifetime of standing in a stronger twin's shadow. Once the detective has entered that inner life, the culprit tends to confess, because he is speaking to someone who already understands rather than to an accuser.