The CDC teams learns the real purpose of the infection and Alan and Julie make a perilous journey to retrieve the canister that has the original source virus.

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 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.

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.

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.

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.