Madame Célerier is determined to marry off her son François to a rich and haughty woman but François has other plans.
A journalist who deals with the column "courier du cœur" has the absurd idea of launching an investigation into the death of a pianist whom he claims to have been murdered. To dazzle his wife, a reporter for the newspaper, he disguises the facts in such a way that the police suspect him, then declare him guilty. It takes a number of adventures to get him out of this mess and get him back into his section.
Between eleven o’clock and midnight one evening, a notorious trafficker Jérôme Vidauban is shot whilst walking in a tunnel in Paris. The case is assigned to Inspector Carrel, who is Vidauban’s perfect double. Using his resemblance to the arch criminal, Carrel manages to infiltrate in Vidauban’s circle of acquaintances and contacts. He becomes embroiled in a bizarre web of intrigue and discovers no shortage of possible murder suspects, all of whom appear to be surprised to see him still alive.