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.

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.