Jean-Pierre (Jacques Villeret), un attaché humanitaire qui travaille au ministère des Affaires Etrangères, accepte de reconduire un jeune clandestin (Lorant Deutsch) dans son pays d'origine. Celui-ci appartient à la tribu des Hommes Gris d'Irghiz, réfugiés depuis la préhistoire dans une cité interdite du Haut Atlas.

From his offices in Switzerland, Russian Igor Lipovsky is engaged in a vast and profitable gunrunning operation with Africa. The French government wants to hinder the activities of the arms dealer and sends a team to sink one of his ships heading for Angola with a load of illegal weaponry. Lisa, Brisseau, Loïc, Tony and Raymond are professionals: they carefully set up their cover, plan all their moves meticulously, and carry out orders without asking questions. Perhaps they should. The code-name of the mission is "Janus"; and just like with the ancient deity, there are two opposite faces for every aspect of the operation: the objective of the French government, the role of each team member, the presumed friend and the assumed foe...