The engines race towards what they perceive as the end of the rainbow to find the supposed treasure, but it always changes location whenever they get close. Once they actually reach it, Thomas and the others realize that sometimes, the real treasure can only be realized when the bigger picture is seen in full.

"Based on the episode "Chasing Rainbows" by Brandon Violette. Based on the Railway Series by the Rev. W. Awdry." At head of title: Thomas & friends, all engines go.