The rulebook contains everything needed to play. After a short introduction to roleplaying games, Mask creation is explained (the Mask is the avatar players use for entering the patient's Intracos). The next chapters introduce the rules, including wounds (and healing), the experience system and the different powers available to the players in the Intracos. The rest of the book contains gamemaster aids (information about the impact on the patient of violence in the Intracos, how to play NPCs, tips on setting the proper atmosphere during the game session), scenario ideas (curing phobias, finding vital information in the Intracos of a criminal, dealing with the split personality disorder of a D&D player...)
The book end with 2 scenarios, "Cas 101: l'homme qui avait peur du noir", and "Cas 102: le prêtre qui avait peur des enfants", and a character sheet.