Dr. Alan Farragut and his team of CDC scientists are called to a remote Arctic Research Base where his brother got infected with a deadly and unknown virus. Soon Alan and his team have to realize that there are secrets being kept.
On day 3, Peter seeks Alan's help before he collapses, Sarah finds a rapid response test for infected patients, Julia begins to slowly feel the effects of Peter's attack while Balleseros helps Doreen get another monkey sample.
On day 4, the quarantined people on Level R force Dr. Hatake to re-etablish communication by cutting off the air supply. Meanwhile, Peter's condition worsens quickly, forcing Alan to try the untested universal treatment, Sarah has to question her rapid response test and Doreen gets closer to figuring out Balleseros.
On day 5, Alan tries to find out what happened to Doreen after discovering her body, Julia finds a helpful friend on Level R, Sarah keeps hiding an infected patient in her room and Balleseros tries to find the mysterious Dr. Hvit.
Secrets come to the light and unlikely alliances are established; at the same time, Alan and Walker take on a dangerous mission to destroy what's left of the NARVIK virus. Walker learns something world shattering about her past.
Alan and Julia travel to an abandoned satellite station in a last-ditch effort to call for help. Once there, they come across the truth behind Hatake's plan and Julia's condition. Meanwhile, Dr. Jordan (Sarah) makes a startling discovery of her own, which could mean a cure for cancer.
Peter Farragut and vectors attempt to spread the virus in a desperate, final attempt. Meanwhile, the scientists of the CDC create a cure for the virus by working together, just as a threat from deadly mercenaries of the Ilaria Corporation threaten their very lives.
The Scythe is revealed to be the immortal Spencer Chiswick, Constance Sutton's 16-year-old son. Alan and Hatake lure Spencer and one of his agents outside where they plan to lay a trap; Hatake throws a canister, allegedly containing the virus, onto the snow and causes one of Spencer's operatives who attempts to retrieve the virus to fall into a chasm. Spencer learns Julia is Hatake's daughter and abducts her. He gives Hatake a choice of lives to save—Julia's or Daniel's, but Daniel sacrifices himself. Julia realizes that a package Spencer brought with him contains her mother.
Balleseros agrees to hand over the virus, already reported in Puerto Rico, if Hatake turns over the list of displaced Inuit children. Peter is revealed to be working for Ilaria and frees the Scythe, who blows up the base, stealing both the virus and cure. He also takes Julia hostage, after killing her mother.