With Magnus's health in the balance, Will, the temporary executive of the Sanctuary, decides that they must show Adam the map of Hollow Earth - the last hope for saving Magnus's life. With minimal fuss, Adam pinpoints a key sequence that reveals a diagram of the keystone - the artifact necessary to find the gateway to Hollow Earth. The diagram contains a number sequence, which Magnus deduces is a set of coordinates, and she and John teleport to that place while Tesla devises a shield needed to protect anyone with Source blood from the defenses of Hollow Earth, Bigfoot prepares for a midnight vigil for his late friend, Father Jensen, and Will runs the international system of sanctuaries.
After overcoming several obstacles, John and Helen return to the Sanctuary with the keystone, which tells them that the gateway is in Tibet, but that's just step one of many in getting into the city. Tesla has devised a shield, but he's only been able to make one of them, instead of the three they would need for all Source blood carriers. And Will is trying to solve the mystery of a missing case of cipher beetles. Bigfoot, Kate and Henry find the driver - dead - and discover that the beetles have been dosed with a bacteria similar to rabies, that makes them and anything they bite turn violent.
But things get even more complicated when Abby, an FBI agent and Will's old colleague, shows up trying to string together some mysterious cold cases, one of which is the murder of Father Jensen. After her persistent pleas, Will relents and looks at the cases with her, but can't tell her what he and Kate later discover: That all of these deaths were caused by microscopic Abnormals in the blood that react to various stimuli. All victims had admitted to killing someone, but said they'd been coerced, then died mysteriously. Working further, Will discovers that all of the victims were related to the Abnormal community somehow, and in a flash realizes that Father Jensen's vigil is sure to be the next target.
Bigfoot, Kate and Will run to the church, where Father Clark is preparing to welcome dozens of Abnormals. Bigfoot, tipped off by an unwelcome scent in the air, tests Father Clark on his relationship with Father Jensen, and discovers fraud. Caught in his lies, Clark opens the vents, releasing hundreds of fierce cipher beetles, and dashes from the room. But Abby has been staking out Clark, and sees him exiting the rectory, pursued hotly by Bigfoot. She catches up to them after Clark has shot Bigfoot, and after Bigfoot has strangled the man to death in vengeance for killing Jensen. Abby brings the Big Guy back to the Sanctuary to recover, and Will gives her at once his thanks and his trust.
And now the real adventure begins: Getting Magnus to Hollow Earth so that she can save herself, Adam, and, as Adam has darkly hinted, Gregory Magnus.