 While sailing the oceans with the two steam locomotives Emma and Molly to the desert where lives, Jim and Luke stop to help out a mermaid named Sursulapitschi and her father, Lormoral, the king of the seas.This leads to a precarious encounter with the Magnetic Cliffs, whose magnetic pull can be turned off and on.When on, they activate a phenomenon called the Sea Glow, which illuminates the bottom of the sea, but also activates the magnetic pull, endangering passing ships; so someone must be found to ensure that no ships are endangered while the Sea Glow is switched on.