The strigoi are evolving, becoming faster. Smarter. Eph struggles to improve his failing bioweapon while trying to work through the emotional fallout of the abduction of his son, Zack. As Setrakian and Quinlan attempt to crack the Lumen's deepest-held secrets, Fet helps a Navy SEAL team in a deadly mission: search for the Master through the underground tunnels of New York.

The Master’s offer to return Zack plagues Eph as he considers taking the deal. Dutch reunites with an old group of friends but begins to question if her safety is better with them or with Fet, Eph and Setrakian. Palmer strives for answers to Setrakian’s secret strigoi blood treatments and discovers he may have a way to acquire it.

The Occido Lumen is gone. Stolen. Setrakian and Fet race to recover it. Gus and Angel try to hide a secret houseguest while avoiding a police sweep, and Quinlan's thirst for vengeance is revealed.

Things have changed. The infection enters a new phase. Fet wants to celebrate, but Setrakian and Eph are worried there's more work to be done. Justine conscripts a new, unwilling army in the fight while Eichhorst angrily lashes out with a plan to strike back.

New information from the Lumen forces Setrakian to seek help from his lifelong nemesis, Eldritch Palmer. Eph's new experiments to understand strigoi communication seemingly take him to the brink of madness while Fet is on a mission to discover strigoi movements across New York City.

Fet strikes hard at the heart of the strigoi army while Justine embarks upon a risky mission to drive the strigoi out of Manhattan once and for all. Gus and Angel fight for their lives and their freedom but are faced with a moral dilemma.

Setrakian offers hope in a new plan to trap the Master while Eph and Dutch seek out the Master's “voice.” Palmer needs Setrakian's access to the white to hold up his end of their bargain.

The Master's voice proves to be more powerful and potentially fatal than Eph or Dutch anticipated. Fet and Setrakian track down the cargo from the Egyptian vessel and realize they may be in over their heads. Quinlan strikes a deal with the Ancients, but a last minute betrayal proves deadly.

Humanity teeters on the edge of destruction. The Master finally reveals himself, initiating the end game of a battle in which there can be only one winner. Eph, Fet, Setrakian, and Dutch must overcome their personal differences in a last-ditch effort to vanquish the strain.