At the request of his superiors, Commissioner Maigret goes to the seaside resort town of Étretat to investigate an attempted poisoning of an elderly lady, the widow of a man who once was quite wealthy. That one day—her birthday—when guests appear in her home, the attempt occurs: someone adds arsenic to the broth the woman drinks overnight, but the victim turns out to be the servant instead. Maigret will have to, as always, immerse himself in the atmosphere and reconstruct the sequence of events, pointing to the culprit.