When trouble strikes at the Blue Mountain Quarry, Thomasis sent to help his Narrow Gauge engine friends. While shunting and hauling, he discovers a mysterious small green engine hiding in the tunnels. Thomas is determined to get to the bottom of the mystery but discovering the truth is harder than he imagined!
Why is the little engine hiding? Will The Fat Controller send Thomas's new friend away from Sodor forever? Travel on an exciting journey with Thomas and friends in his biggest movie ever, tracking down clues, discovering lost engines and revealing the power of friendship!