Bobo and Fuffa are playing at being a skytrain, with Fuffa as the train and Bobo as the driver. They tear around the Skyworld causing trouble until Baba Yellow tells Bobo that if he calms down and is good, she will take him on a ride on the real skytrain later. Bobo and Skydonk go off to find something to do. Each time Bobo is tempted to be naughty, he dutifully doesn't and returns each time to Cloudyhouse to ask if it's time to ride the skytrain yet. Baba Yellow eventually tells him to wait by the skytrain bell until she is ready, but not to ring the bell. This proves to be a temptation too far. Bobo rings the bell and summons the skytrain. He jumps in with much delight and as it picks up speed, he is joined by Fuffa and Little Star. But the train goes faster and faster and Bobo can't control it. The Cloudbabies are alerted to their predicament and corrall a bank of clouds as a buffer to slow the train down, but to no avail.

Bobo will unbedingt einmal Lokführer sein und den Wolkenzug fahren. Die Wolkenkinder haben es ihm zwar nicht erlaubt, weil es zu gefährlich ist, allein darin zu sitzen. Doch als er vor der Glocke steht, mit der man den Zug ruft, kann er nicht widerstehen und läutet sie. Zuerst macht ihm die Fahrt im Wolkenzug einen Heidenspaß. Doch dann gerät er außer Kontrolle.