On Christmas morning, Maigret and his wife are enjoying a rare peaceful holiday at home in Paris when they are visited by two women from their apartment building. One is Madame Martin, a young widow, and the other is her neighbor, Madame Doncoeur, a retired schoolteacher.

Madame Martin’s daughter, Catherine, has told an odd story: during the night, she awoke and saw Father Christmas in her room. But instead of bringing gifts, he appeared to be searching for something. The women are disturbed—not by the fantasy—but because they suspect someone actually entered the apartment.