On September 7, 1911, Guillaume Apollinaire is arrested in Paris and taken to La Santé prison. For two weeks, police have been hunting for the Mona Lisa, mysteriously removed from the Louvre. The poet did not steal the Leonardo da Vinci canvas, but his links to Géry Pieret, involved in several museum thefts, place him at the center of an inquiry that will also reach his friend Pablo Picasso.