An alternate universe of Equestria Girls set in the world of Thomas the Tank Engine.

Sir Topham Hatt leaves Miss Celestia in charge of the North Western Railway while he is off on an important holiday. During her tenure as temporary controller, the new locomotive Diesel 10 and his driver Discord arrive to cause chaos for the North Western steam engines. Through all this, Miss Celestia realizes her gold dust supply is depleting.

Meanwhile, Twilight Sparkle and her adopted brother Spike visit their brother Shining Armor and his wife Cadance, who live on Muffle Mountain away from the railways. Unknown to Twilight, however, something precious to her brother is under threat of destruction by an old foe named Quinn Chryssa "Chrysalis".

Twilight and Spike, with the help of five other teenage girls, Miss Celestia, and Thomas the Tank Engine, must help Shining Armor and Cadance to once again believe in the world of hope, since they hold the key to the magic of Sodor…

Told in the first person from Twilight's perspective. Rated for Everyone, but there are slightly mature themes.