A research team are taking measurements of an underwater eruption. They discover a fissure that appears to lead all the way to the Earth's core. While the discovery is exciting, what exists in that fissure could lead to deadly consequences.

A manned probe is returning to Earth when it is suddenly caught in the grip of a strange force and destroyed. Investigations point to a secret Chinese installation being responsible. Capt Crane is tasked with locating the base and destroying it.