Полгода без толку обивает пороги Сыскной полиции молодая парижанка Сесиль Пардон, встревоженная тем, что в квартире, где она обитает вдвоём с тетей-инвалидом, по ночам бывает кто-то посторонний. Не слишком доверяет словам Сесили и комиссар Мегрэ, хотя он не видит оснований считать девушку сумасшедшей. Однако убийство тёти и необъяснимое исчезновение самой Сесили заставляют комиссара вспомнить все подробности её рассказов и ближе познакомиться с историей семейства Пардонов.
Noël Bienvenu, owner of a career, is a widower and lives with his parents. His son Bastien, whom he despises, was sentenced to six months in prison for theft. Noël goes to see a dying friend, Romieux, who asks him to take care of his daughter Marthe, who has settled in Paris (Batignolles district). Noël goes there and discovers that Marthe is destitute (her lover Gaston being an incarcerated mobster): he then offers her to come and live with him and soon, marries her.
A struggling artist buys a talisman that gives him love, fame and wealth. The talisman is a severed left hand, and it works perfectly, in fact, magically. But of course there is nothing free in this world, and after one year the devil comes and asks for his due.
Dédé de Montmartre, former king of the accordion, has become a bad boy who lives off drug trafficking and prostitution. He sets his sights on a young girl, fresh and naive, Odette, saleswoman at Galeries Lafayette. But he is touched by the charm of this midinette.
Ignace Boitaclou, although sympathetic, is not very intelligent. Upon his arrival at the barracks to perform his military service, he was appointed colonel and had to take care of the latter's terrible wife.
