A troubled Baltimore FBI agent becomes involved with a secret government unit assembled to hunt a group of ruthless terrorists, who may or may not be from this world, and who may or may not be involved in his wife's disappearance.

Flynn and the ETU investigate violent attacks on U.S. soil, and discover the Hunters are working with human collaborators.

After a succumbing to a particularly nasty Hunter urge, young Regan learns the truth about what she is from her father ... and his knife.

Flynn stumbles upon startling new information about his wife, which leads the ETU to a suspected human-hunter collaborator, while Flynn finds himself in an unexpected confrontation.

The ETU's discovery of the name and suspected location of a High Value Target, dredges up old memories for Jackson. Meanwhile, Flynn, Regan and Briggs attempt a daring raid on a Turkish prison.

The Hunters attempt to "reprogram" a captive Regan. While the ETU work to locate their missing agent, they deal with the possibility that there could be a mole in their ranks.

Regan discovers that she wasn't told the truth about her father's disappearance. Meanwhile, Flynn and Briggs race against the Hunters to acquire a scientist critical to "The Purge."

Flynn (Nathan Phillips) struggles with his self-destructive downward spiral, Regan (Britne Oldford) confronts her mother, and the Hunters make last-minute preparations for The Purge.

Flynn (Nathan Phillips) faces his demons by visiting the only other Marine in his platoon to survive their captivity in Afghanistan. Meanwhile, the ETU discovers that Emme (Shannon Berry) might know too much.

The ETU finally cracks the Hunter language, allowing Finnerman (Sarah Peirse) to set a trap. Regan (Britne Oldford) questions whether all Hunters are terrorists, or whether some may be innocents living among us.

In the fallout of the Hunter roundup, Jackson (Lewis Fitz-Gerald) and Finnerman (Sarah Peirse) are at odds with each other. The ETU's only hope of stopping The Purge is to make a risky move on the Hunter's weapons' supplier, Viktor Karp (Erroll Shand).

With The Purge imminent, the ETU has no choice but to trust an unlikely informant, leading all paths to converge at the primary Hunter base for a climactic showdown.