Codeine has been stolen from Philippe Calaro's pharmaceutical laboratory. The police are investigating and ask the young chemical engineer to remain at their disposal, as one of his direct employees is under suspicion. On his way home from an evening out with a friend, whom the case has forced him not to accompany on a trip, he discovers the corpse of an unknown man in the boot of his car. Distraught, and without thinking about his imprudence, he disposes of the cumbersome and inert passenger in the woods of St-Cloud. After the departure of his girlfriend's plane to Orly, he is accosted by a young girl who tells him she knows the dead man from the previous evening, and begs him to join her on the Air France bus, to disguise the fact that he is being followed.