Locomon crashes into the real world as a runaway train, and the tamers have maybe an hour to stop it before it tears open the barrier between worlds. The entire movie is velocity, no filler, no setup stretches, just kids on bikes chasing a digital locomotive that doesn't care about their protagonist powers. This is what happens when the Digital World doesn't wait for a plan.

A train Digimon called Locomon suddenly appears in the real world on Rika's birthday, just as the other Tamers are secretly planning a surprise party for her. With the locomotive heading for the gateway into the Digital World, the Tamers rush to halt it before it gets there. While her friends fight the train, Rika is drawn under the mind control of the villainous Parasimon, who manipulates her through memories of her father, and even Renamon struggles to reach her. The movie mixes Digimon battles and sci-fi adventure with lighter comic moments.