In Paris, an elderly man is found with a gunshot wound to the head, having completely lost his memory. A few days later, it turns out that he is a former captain, now managing a port. Commissaire Maigret escorts Captain Joris home, but that same night he dies from poisoning by strychnine. As before, everyone around is hiding the truth, and Maigret has to go in the dark—step by step—through dense fog, observing, comparing, and piecing together details to restore the true picture of the tragedy…