Fearing the theft of an important secret formula, the scientist Claude Amory asks for help from Monsieur Préval, director of the Sûreté. But when Amory is mysteriously poisoned inside his own home, the detective realizes the case is more serious than he had imagined and decides to investigate each of the suspects.

Here's a railway station. Next to it, there's generally a town; and in a town,there is love! The train arrives. Mr. Andrieu is expecting his sardines and both his daughters, back from winter sports.