The small town of Solaris is nestled in a place far away from the rest of Equestria. The major rail network doesn't even count it as a place on their maps. The hope of the town rests on one little locomotive that was forgotten just like them. That engine...is Sunny.

(The locomotive is based on the concept of Ivor the Engine. She cannot speak because of no face, but has the ability to get its points across.)