Eph and Nora experiment on their newfound patients. Fet and Dutch grow closer as they clear out the neighborhood buildings, and Kelly begins her hunt for Zack.

Gus and Vaun wage an attack on Palmer as Eph struggles to connect with Zack. Councilwoman Justine Faraldo vows to bring her extermination policies to the other boroughs.

Eph and Nora finally see their lethal virus in action. Fet takes the security of Red Hook into his own hands while Dutch and Setrakian set off for Staten Island to question Fitzwilliam, Palmer's former body guard.

Eph changes his appearance to leave the city while Nora is left as the reluctant parent for Zack. Dutch and Nora make a deal with Justine to secure Fet's release from jail.

Eph concocts a plan to make and distribute a bioweapon. Gus realizes Angel can be an unlikely ally, and Kelly comes after Nora and Zack.

Justine takes drastic measures to counter a surprise invasion. Nora and Fet perform a useful mission while Eph and Setrakian face off against an old foe.

Eph and Dutch work together to thwart the Master's greatest ally. Justine runs into trouble with the Mayor while Setrakian tracks down the real owner of the Lumen.

Eph must choose between Zack's safety and the safety of the citizens of NYC. Meanwhile, his relationship with Nora reaches a critical impasse, and Gus and Angel assemble an unlikely gang of Sun-hunters.

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.

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.

NYC is falling. Eph and Dutch frantically race to finish their new device to stop the Master before the city is overrun. Justine, Gus, and Angel fight in one last stand to stop the spreading virus. Palmer extracts vengeance for past wrongs but may have crossed the line.