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 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.

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.

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.

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.

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.