It's so busy on the island of Sodor that Sir Topham Hatt needs to bring in some new engines to keep the railway running smoothly. There is Spencer, the fastest express engine the island has ever seen. Meet Emily, the sleek green engine with the beautiful brass dome. And new friend Arthur, whose spotless record gets ruined when Thomas plays a trick on him. Join Thomas and his new friends for train loads of discovery and fun.

When trouble strikes at the Blue Mountain Quarry, Thomas is sent to help his Narrow Gauge engine friends. While shunting and hauling, he catches a glimpse of a small engine trying to hide, yet no one will provide any clues to the engine's identity. Thomas is determined to get to the bottom of the mystery, but discovering the truth is harder than he imagined! Will Thomas be able to save his new friend? Or will the mysterious engine be sent away from...

Take the plunge with Thomas and his friends! Oily Diesel gets Percy all wet, while Gordon suffers the embarrassment of losing his buffer.