A sapient rabbit named Mimio is born in an university lab experiment. However, Mimio thinks he is human. Mimio escapes, and finds refuge under John, a kid scientist. John, who had lost his father, is constructing a train capable of penetrating the earth's core, allowing for safe transportation.

Initially, the train runs fine, but it stops at the Earth's core. When they get out, they are swept away by groundwater...

What lurks below the surface? Will Mimio and John survive?