Magnus responds to an anonymous call for help at an abandoned building. But when she gets trapped inside, she discovers whoever made the call has a very different agenda.

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.

Will takes command of the Sanctuary while Magnus and Druitt search for a critical artifact in London. Knowing that Magnus's only hope for a cure lies in the secret subterranean city, Will ignores her warnings and releases Adam-Hyde in the hope that he will lead them to an access point for Hollow Earth.

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.

Magnus is revived to answer Ranna's questions and soon figures out that despite Ranna's efforts the city is in great deal of trouble and the fall of Praxis could also threaten the surface world however Magnus is able to help. Magnus and Ranna makes an understanding to help and she revives rest of the gang. Magnus manages to save the city with the help from Gregory Magnus meanwhile Will tries to breakdown Adam's plan that can cause huge trouble.

Receiving word that a large group of Abnormals has been spotted near a South Dakotan cave entrance, Magnus realizes it's the first wave of Abnormals emerging from Hollow Earth.