Marc Thiriez (Vincent Lindon) is an architect who's worn a mustache for many years. Now approaching middle age, he decides to shave it off, naturally expecting others to notice. But when his wife, Agnes (Emmanuelle Devos), ignores the change, he's perturbed. When he asks why, she insists that he hasn't had a mustache for years. When he confronts other friends and colleagues about it, they too tell the same story. As Marc grows increasingly paranoid, his loved ones consider having him committed.