When a teacher is found dead, having apparently committed suicide, his friend and colleague takes over class 4F and finds himself responsible for a group of subdued, well-behaved and yet strangely menacing pupils. Assuming their behaviour to be a response to the trauma of the event, Pierre Hoffman at first grants leeway to the precocious class, refusing to embrace the hostility felt by other staff members towards the children. Over the weeks that follow, however, he receives a series of signals and warnings that cause him to question the motivations of his pupils and the circumstances of his colleague's suicide. Clara Sorman - a pupil known among the staff for having lost her virginity at the age of nine and organising 'special' sex evenings - suggests that Hoffman resign as soon as possible. Then a parcel is delivered to his house, containing a small stuffed toy filled with worms, and he receives anonymous phone calls, a mixture of heavy breathing, hysterical laughter and sinister music. Over the school holidays, Clara Sorman is violently attacked, but she claims to remember nothing about her attackers. Steeling himself and refusing to believe that the situation can be any more sinister than his suspicious imagination, Hoffman applauds and supports class 4F's decision to organise a school trip to the Normandy coast. Only once the trip has begun, however, does Hoffman begin to understand the extent of their bizarre solidarity and their ultimate goal.