S1, E1: Someone is drawing mustaches on the great works of art at the Louvre Museum! Cousin Gaston needs the mice to help him find out who is responsible before the museum is closed and his friend Emily's father, the janitor at the Louvre, loses his job. At first, all clues lead to the artist, Monet, but soon our heroes discover it is Louis Moustache, a frustrated rat artist, who is defacing the paintings. Together they convince Louis to clean up his act (and the great works) and help him launch his own art opening for the mice elite of Paris.