Locomotion, a unicorn colt who used to live near Trottingham, is a keen railway enthusiast, and spends most of his time tending to the engines at Ponyville Sheds. One day, shortly after his latest cleaning turn, he is approached by a famous filmmaker from Canterlot who offers him the lead role in his latest production, a role that he eagerly takes up.

But while he and his friends, including the Cutie Mark Crusaders, are taking part in the film, strange goings-on have been hampering the production. Can Locomotion and his co-stars solve the mysteries and save the movie, or is his first appearance on the big screen going to be his last?

Told in the first person by Locomotion himself.