Themroc, a bachelor house painter living at home with his mother, leads a sad and colorless life. One day, after a run-in with his boss, he rebels. He wrecks his apartment, rejects every facet of bourgeois life, and begins acting like an urban, modern-day Neanderthal.

Célèbre pour ses personnages affables et bourgeois, Michel Piccoli subit une métamorphose bestiale dans ce film provocateur de Claude Faraldo qui se passe entièrement de dialogues. Ne comprenant que des grognements et des gestes, Themroc est un cri de guerre antiestablishment et anticonformisme.