Thomas the Tank Engine and his friends are being threatened by diesel engines like the surly Diesel 10 and his sidekicks Splatter and Dodge. Even the magical Mr. Conductor, who has always traveled between the train world and the human world of Shining Time Station, is losing his powers and sparkle. In the middle of this crisis, Lily meets up with Mr. Conductor on the way to visit her lonely grandfather Burnett Stone. Brave Thomas reminds them all that "even little engines can do big things."