Thomas獲肥控制員派到藍山石礦場工作,發現陌生的小火車Luke躲在山上的洞穴,Luke告訴Thomas一個驚人秘密:原來他初到索多島那天因搶先上岸,竟使同行的黃色火車掉進海裡,凶多吉少!Luke害怕被逐出索多島,於是一直躲藏起來。為了助新朋友重獲自由,Thomas決定要查明這宗古怪事件…When the Fat Controller sends Thomas to work at the Blue Mountain Quarry, Thomas spots an engine he has never seen before trying to hide. Determined to get to the bottom of the mystery, Thomas tracks down and befriends Luke, who tells Thomas he is hiding because he did something so bad, he could be sent away from the Island of Sodor forever. Thomas does not believe this and sets off on a journey to discover the truth behind the story of the poor runaway engine. On the way, he learns of engines brought to Sodor from faraway lands and of an accident at Brendam Docks where an engine fell into the sea. But only when he has learned every piece of the story, can Thomas convince his new friend that there is no reason to hide.