Mathias, whose dead father was a diplomat in Germany, decides to study the forensic medicine in Paris. In the train, he has some troubles with the border police, and is insulted and threatened by a strange man, who disappeared quickly. Next day, he discovers in his luggage a shrunken human head. He soons becomes fascinated by it, feeling responsible (sentry of the memory of the head's owner) and starts his own investigation. What will leads him to cope with French secret services.