Thomas tells Duck, Stepney, Percy and BoCo that Stan Marsh is looking after them while Sir Topham Hatt is on Vacation. Stan Marsh appears. Percy refuses to help Stan, claiming that smart people is just for engines and that "students don't control engines and students don't head them." That night, Percy wishes for a real adventure for that summer, and to do something no one has done before. A shooting star deposits a large colorful egg in the shed, which is accidentally knocked onto a birdseed truck by Percy and is carted off. Stan heard that the egg is kidnapped by an evil monster. Stan and the engines begin their adventure to recover it through a parade. Stan's brother figure Eric Cartman catches it when it almost lands on the ground and breaks. Duck says "Well, What are you waiting for? Let's go." like Elliott says if for "E.T." Stan and the engines chase the egg throughout a moutain railway, a circus, and puff with a jet engine while continuing their pursuit of the egg. Cartman, Kyle and Kenny arrive just in time to see the egg hatch. After they return the egg to the barn, it finally hatches. Percy comments that the egg looks like a rainbow.
The egg is a koala-like dream maker named Twinken who shows everyone Duck's dream and then Stan's. Percy apologizes to Stan for being mean to him and admits he thinks he's cool. Stan accepts his apology and tells Percy he thinks he's cool also and the two share a hug. Twinken shows everyone a magical fireworks display which lands in Stan's arms. Stan, Kyle, Cartman, Kenny and the engines thank him for being rescued. The film ends with Cartman saying ""Aw, god dammit!!"
- Trey Parker as Stan and Cartman
- Matt Stone as Kyle and Kenny
- Martin Sherman as Thomas and Stepney
- Kerry Shale as Duck and BoCo
- William Hope as Percy
- This is a South Park/Thomas crossover.