Alan, Kyle and Winger search the woods for the tree with red sap that might be a cure for the pathogen.

The Abbey becomes a house of horrors as Kyle struggles with his infection and Anne begins to shape a successor to Michael.

The Navy prepare to implement Plan B, a final solution to ensure that the virus and everyone infected with it never make it off the island.

As Michael struggles to keep the abbey under control, the CDC team moves closer toward tracking the source of the pathogen. Alan fights the urge to rejoin his team and confronts the reality about Peter’s allegiances. In the future, Walker makes a desperate attempt to escape from her delusional father, with potentially deadly consequences.

Amy creates an outbreak of the disease. Michael torments Peter in the pit. Alan, Jordan and Kyle discover the truth about the Abbey's food chain. An uprising at the Abbey threatens the safety of the uninfected. In present-day Paris, Balleseros meet an unlikely immortal.

The uninfected are hiding in a secret bunker on the base as the CDC attempt to retrieve the canisters with the virus and the cure while the Ilaria assassins capture Hatake and force him to chose between which one of his children they will kill first.

After Daniel leaves Balleseros to die, the mystery surrounding his connection to Hatake is revealed. As he works to save Peter, Alan struggles with his feelings for both Walker and Jordan.

Peter and Jordan leave the safety of the Abbey to retrieve some specimens and discover just what’s living in the woods, meanwhile Sister Amy plots to make them leave forever.

Michael locks Peter and Alan in a pit. Alan escapes and discovers that Kyle has a secret of his own. Agnes reveals a shocking truth to Michael, who drastically turns on her for doubting him. In the future, Caleb uncovers Walker's deception and takes matters into his own hands.

Kyle rescues Dr. Sarah Jordan as Alan Farragut fights his own brother, Peter Farragut.

As Dr. Alan Farragut accelerates the hunt for his infected brother Peter, the quarantine of three scientists threatens to create panic at the lab. Doreen finds evidence that Dr. Hatake is lying about his research.

As Alan sets up an isolation unit to quarantine the infected lab workers, Walker and Jordan each face the possibility that they have the deadly virus, too.

The CDC team continue to investigate the island; at the same time, they discover Peter's brother, Alan, is a member of Brother Michael's cult, and his warnings for them to leave the abbey fall on deaf ears.

A Center for Disease Control medical team's investigation of a disease outbreak at a high tech arctic research lab uncovers the truth about a secretive research project that could threaten the future of humankind.

As Alan's controversial cure leaves Peter clinging to life, the unchecked virus forces Jordan to make a devastating decision. Walker discovers the surprising truth about her new ally, while Daniel squares off against Balleseros.

In a last ditch effort to find help and a cure, Alan and Julia go to an abandoned satellite station discover a shocking secret that reveals Hatake's ultimate goal and the reason why he has developed the deadly virus.

The Vectors start working together to hunt down the uninfected as the CDC develops a risky cure and a band of assassins from Ilaria secretly infiltrate the base.

The uninfected are hiding in a secret bunker on the base as the CDC attempt to retrieve the canisters with the virus and the cure while the Ilaria assassins capture Hatake and force him to chose between which one of his children they will kill first.

The Coast Guard arrives on the island to take the CDC team to another island to deal with another outbreak of the pathogen. Meanwhile, Sister Amy has to contend with Brother Michael and his plans.

As Alan risks killing Peter in a desperate effort to cure him, Walker teams with a mysterious young researcher to survive their quarantine. Jordan discovers her Rapid Response test is flawed.

As Ilaria CEO Constance Sutton arrives to collect the virus and its cure, Alan finds Walker seemingly symptom-free. Daniel learns the truth about his "adoption" by Hatake.

Alan and Peter capture the assassin Scythe and demand to know the whereabouts of Julia's mother. Balleseros confronts Hatake about the missing Inuit children, while Anana and her brother learn of Daniel's fate. Concerns that the virus is in Ilaria's possession again forces Alan and the team off the base to search the world in order to retrieve it.

15 months after the events at Arctic Biosystems, new CDC team with the addition of biotoxicologist Kyle Sommer respond to a potential outbreak on a Windjammer in the Northern Pacific. Their search leads them to an island occupied by a mysterious cult led by the charismatic Michael. Meanwhile, 30 years in the future, Walker arrives at the same island searching for Alan Farragut.

Alan risks his life to save his brother Peter from Ilaria CEO Constance Sutton, only to see him re-captured by Vectors. Julia Walker deals with the mystery of her "cure" while her half- brother Daniel confronts their father, Dr. Hatake, about being abducted as a child.

As Peter gains a new cellmate, Michael takes extreme action when his followers begin to mutiny.