When a traumatized mining foreman is placed under the psychiatric care of Dr. Vincent Armstrong, the doctor thinks he has started just another shift. But as the victim begins to remember what drove him temporarily insane, Armstrong’s interest becomes personal, and he makes a series of discoveries that threaten to tear apart his carefully constructed scientific view of the world, and show in horrifying clarity that his patient is anything but delusional.

As Armstrong’s world falls apart, his recovering patient learns that he has not escaped the horrors he encountered underground, and that no place on earth is truly safe from the “Tunnelers.”