The story opens in a Western saloon, where a young musician with a banjo begins to tell a tale of Lucky Luke and his sworn enemies the Dalton brothers: Joe, William, Jack and Averell. Luke has, once again, as he has done many times before, thrown the four outlaws into jail. The prison is also the abode of a guard dog named Rin Tin Can (Rantanplan in the original French language version).
Monsieur Tête, an ordinary bureaucrat, rebels against the world and the ideas of the people around him. Because of his marginal behavior, his head is broken, like everyone else.
This is the story of an obsession. Mona Lisa keeps smiling quizzically while our poor hero is pursued by her representation in all its forms, in all places. She smiles at him in a museum, at a bookseller along the banks of the Seine, in the streets, at a café. Enough to drive him up the wall!
