When Caillou visits Clementine, he is impressed to see Billy practicing on a Tuba. Billy shows Caillou and Clementine a little bit about the tuba and plays a musical game with them. Soon, Billy’s marching band mates arrive to practice. Clementine and Caillou wish they could join in too. They make their own pretend horns with cardboard tubes. When Billy’s sheet music is lifted away by a gust of wind, Caillou catches it and saves the day for the band! They all march on, giving Caillou a musical escort back to his house. (thetvdb.com)