When Caillou visits Clementine, he is impressed to see Billy practicing on a Tuba. 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. Also, on a winter evening, a strange sound grabs Caillou's attention. He follows the sound to find out its source. Caillou continues his search and discovers Gilbert in his room, having a great time playing with a baby toy. Later, Caillou goes up to the attic with Mom and finds a box containing a teddy bear and a music box. Caillou and Rosie find a way to share these treasures. Caillou gets a special invitation to go to Andre's gym class. A little intimidated at first, Caillou tries his best and ends up having great fun. Caillou finds the leap-frog exercise difficult but he keeps trying and finally succeeds. Caillou learns to deal with a change in plans, when Daddy has to use the car and Mommy and Caillou have to take the subway. Caillou has fun checking out the map, getting tickets and listening to the musicians! In fact he has so much fun, he and Mom decide to take the subway home!