Amy Larson and Hunter Forrest are enjoying the last days of a Key West vacation when they learn that there have been disappearances in Denver, and an agent friend of Hunter’s has found a little black plastic horse on his porch. It's clear the doomsday cult they've been tracking is sending a deadly message. The two head to Colorado to investigate the disappearance of a young woman who never returned from a hike. One of the woman's co-workers reported her missing and has persisted in getting law enforcement involved. Having received the little horse, Andy Mason, Hunter’s old friend, followed up on the report; and as soon as Amy and Hunter land they all head to the caves where the woman was exploring. There Amy and Hunter split up at a fork in the caves and she is the first to discover a strange black hole filled with dozens of bodies.