Determined to prove his importance on Sodor, Thomas takes James' trucks and sets off on a big adventure to the Mainland. On the way he makes friends with the cheerful and helpful "Experimental Engines" but, after a wrong turn, finds himself lost in the steelworks. There, Thomas encounters two mysterious engines who instantly make him feel welcome but who aren't what they first seem... After Thomas fails to return, James sets off to the mainland but runs into trouble himself and it is up to Thomas and the Experimental Engines to save the day. Join Thomas in a tale of daring escapes, heroic rescues and discover that true friendship comes in all shapes and sizes.