With Adam on lockdown at the Sanctuary, Magnus investigates his connection to Hollow Earth - and Druitt - while being forced to reveal dark secrets about the chaotic origins of the Five.

Seeking a gateway to the secret subterranean city, Magnus leads a treacherous mission to Tibet - telling a bitter Adam that he must stay behind while promising to bring back a cure for their radiation sickness. Because of their source blood, Magnus insists that Tesla and Druitt stay behind as well, taking the only shield Tesla was able to construct for herself. The hidden city, however, is rigged with deadly security traps - and death awaits the team at every turn.