After being ambushed at the Cabal's weapons facility, Ashley and Henry find themselves separated and restrained, unaware of the other's whereabouts or safety.
Tied to a chair on an electrically charged floor, Ashley meets Dana Whitcomb, who reveals that the worldwide release of their devastating bio-chemical agent will go ahead as intended, in spite of their attempts to impede the plan.
In a separate room surrounded by Cabal medical personnel, Henry pleads for answers from his captors while strapped to a gurney and hooked up to monitoring equipment. While surgeons methodically work around him, one doctor reveals that they intend to chemically induce his natural transformation into his alter ego, a predatory life-form, permanently.
Magnus, Will, and Druitt, along with Dr. Watson and Clara continue their trek through the overgrown wasteland that was once the beautiful city of Bhalasaam. It is here that they hope to retrieve the Source blood - their one defense against the effects of the Cabal's pending bio-chemical attack.
They know that the last remaining vial of Source blood has been safely protected in the labyrinth under the city, hidden by Magnus's father Gregory. But with the city decimated around them, they become acutely aware that finding the entrance to the labyrinth now seems nearly impossible. In addition, they are still missing one member of The Five. Without Nikola Tesla's presence, they are unlikely to complete the tests that are vital to retrieving the vial.
Magnus, Druitt and Clara prepare to head back to the Sanctuary, feeling temporarily defeated. But Will and Watson convince them to stay, certain that they can reconstruct in their minds, what was once the thriving metropolis before them, and therefore find the entrance to the Hall of Records and the labyrinth beneath.
Using their combined intellect, Will and Watson decipher the location of ancient city's hub and main thoroughfare. From this, they establish where the Hall of Records would have been located a century before. Arriving at their determined coordinates, the team moves away the ruined masonry, overgrown with decades of moss. And just as they suspected, they uncover a passageway with secret access to the central rotunda below.
As they descend into the shadowy cavern, Magnus explains the lore of the ancient vampires who, at one time, retreated to this hidden city to protect their advanced technology and superior knowledge from their enemies.
As she speaks, a voice responds from the darkness. The group is astonished to see Nikola Tesla, the elusive fifth member of The Five, who has been furtively waiting for their arrival in the labyrinth.
They all gather at the center-point of the tunnels where they receive instructions for five challenging tests geared specifically to each of their special gifts. One mistake in judgment or calculation will result in deadly consequences for them all.
While The Five, along with Will and Clara, attempt to overcome the challenges set before them, Ashley and Henry struggle to hold their own against the Cabal in the weapons facility.
But it's Watson, with time running out, who suspects that they are still missing a key element in defeating the Cabal in this battle. Both Magnus and Will manage to discover the Cabal's true agenda, but they are too late to stop their plan from becoming a reality.