A mysterious plague carried by Irathients strikes Defiance, but affects only humans. Fear and paranoia cause the Irathients to be sent into quarantine in the mines.
The town of Defiance is shocked when the body of Hunter Bell, a prominent businessman who disappeared almost six years ago, is discovered hidden at the NeedWant.
In the aftermath of the razor rainstorm and the subsequent arkfall, Nolan and Tommy discover an American astronaut who has been in hypersleep for the past several decades.
Amanda negotiates with the Omec for the future of Defiance. The Tarrs return to find much has changed, and their loyalties are tested between the humans, the Omec, and the Votanis Collective.
With Omec on the loose, Nolan, Amanda, Irisa, Datak, Stahma, Berlin and Doc Yewll undertake a potential suicide mission to end the Omec threat once and for all.
Amanda welcomes an encouraging Votanis Collective delegation to Defiance, Stahma's loyalties are tested, and T'evgin takes another step towards acclimating to life on Earth.
Nolan, Amanda and Irisa search for a way to stop Kindzi from transporting more Omec to Earth. Datak tries to escape from an Omec compound, and Stahma asks for forgiveness.
Kenya is kidnapped when she stumbles onto a drug ring in which Votans are draining humans of their adrenaline - and literally scaring them to death to get it.
Nolan recruits a militia to fight the oncoming Votanis Collective army, but the people of Defiance need convincing to fight in what may be an unwinnable war.
Rafe and Nolan explore underground St. Louis while hunting for an escaped convict. Meanwhile, Irisa and Amanda clash over a violent Castithan tradition.
When the area is hit by a deadly razor rainstorm, the people of Defiance must run for cover and stay indoors, where they discover truths about themselves and their neighbours.
Datak is framed for a bizarre murder and turns to an unlikely ally for help, while Irisa discovers more about her destiny after encountering a mysterious stranger.
Irisa is arrested after returning to Defiance but Mayor Pottinger offers Nolan her release in exchange for capturing those responsible for unleashing a deadly explosion.