In a mystical and enchanting land, the world of talking trains, Thomas the Tank Engine embarks on an extraordinary adventure. The island of Sodor faces a crisis as the magical railway connecting their world to the human world is in jeopardy, threatening the harmony between both realms. The source of this magic, hidden in a lost engine named Lady, holds the key to restoring balance. Meanwhile, in the human world, a kind-hearted man named Mr. Conductor struggles to maintain the dwindling magic that powers the trains and bridges the two worlds. Evil diesel engines like Diesel 10, along with his bumbling sidekicks Splatter and Dodge, are determined to take over the railway systems for their own nefarious purposes.

Lily, a resourceful young girl visiting her reclusive grandfather Burnett Stone, stumbles upon this hidden world. Together with Thomas and Mr. Conductor, they embark on a journey filled with friendship, teamwork, and bravery to unravel the mystery behind Lady and the magic railway. Along their path, they learn vital lessons about belief in oneself and the importance of preserving the spirit of togetherness. As challenges intensify and secrets unfold, they fight against time and Diesel 10's menacing plots to save their worlds from impending doom.