An infamous prison in the Amazon jungle and an underground labyrinth used by a secret police force contain a murderous past; experts investigate the secrets behind these hellish structures to uncover how they were built and why they were abandoned. This is a mashup of S05E06 "Secrets of the Doomsday Caves," S07E01 "Into the Murder Labyrinth," and S05E01 "Jungle of the Damned."