When danger breaks out in the Blue Mountain Quarry, Thomas is dispatched to assist his Narrow Gauge engine colleagues. While shunting and hauling, he notices a small engine attempting to conceal itself, but no one provides any information about the engine's identification. Thomas is determined to solve the riddle, but uncovering the truth proves to be more difficult than he anticipated! Is Thomas up to the task of rescuing his new friend? Or will the mysterious engine be permanently banished from Sodor? Join Thomas and his companions on a thrilling voyage through his largest film to yet, chasing down clues, discovering lost engines, and demonstrating the strength of friendship!