Caillou and Leo are playing with their rocket ships in the park. Rosie wants to help them build the space station but she accidentally wrecks it. Caillou’s frustration builds up when they have to go home because of Rosie’s nap. At home, Caillou and Leo continue their space game and are thrilled when Mr. Hinkle gives them a cardboard box which they transform into a rocket ship. They all work very hard to decorate it. When Rosie comes out to help, Caillou is worried she’s going to wreck it and doesn’t want her help. But with Mommy’s help, Rosie makes the perfect final touch for the rocket ship: a flag! Caillou realizes that Rosie can help too and invites her to join him on the first mission in their new rocket ship!