感染が拡大し、都市を直撃する、致命的なウィルスの原因を突き止めるための時との戦い。患者のゼロを特定して、感染を封じ込めるのはNorBACにかかっている。致命的なウィルスが充分ではないかのように、NorBACの主任科学者、デイビッドは反抗的な10代の娘リリスが突然到着したことと、チームで最も必要になるはずの主席ウイルス学者やNorBACの最高執行役員キャロラインとの安全保障クリアランスをめぐる議論に対処しなければならない。

Lilith befriends Mick, who is dying and desperate for David to help him discover if he really is a clone and possibly save his life. Meanwhile, NorBAC has managed to locate patient zero and must proceed with the interrogations at "Hazmat City." Was this an act of Bioterrism? Caroline is determined to find out who's responsible as more die and one more is exposed. David must now face his fate.

Mick turns to Lilith, who helps him steal evidence from the scientist who cloned him, his own father. Meanwhile, Caroline suggests that Hira has possible terrorist links and shuts her out of NorBAC. David must bring Hira back. But when he does he's confronted with a rally outside NorBAC, lead by a fanatical Reverend who claims that Christ can be genetically resurrected from a Crucifixion nail. The Reverend wants him to prove it, but David's not into playing God. In the frenzy, shots are fired and someone gets hit.

NorBAC investigates an outbreak of prion disease (mad cow) in humans. The victims are spread out across North America. How are the cases connected? In the aftermath of Hiras's death, David is determined to expose the fraudulent reverend from episode 3. David suspects his old friend Danny, a hockey player, is using a dangerous performance-enhancing steroid.

NorBAC reviews an experimental treatment being used on children with Leukemia. Just as they are about to declare the cancer therapy safe, another child dies. David disregards the proper channels and goes to Nunavut to get a sample of what he believes is the Spanish Flu virus from a frozen corpse. Mick and Lilith go whale-watching in Quebec, but Lilith begins to realize just how sick he is.

Carlos Serrano, the Senior Researcher at NorBAC wants to help a friend dying of AIDS participate in cutting edge research. He convinces David to help supply a Houston lab with contraband stem cells in order for his friend to be the first guinea pig for this radical gene therapy. When another child dies, David is determined to find out why the cancer treatment isn't working.

A major power blackout on the Eastern Seaboard leads to fears of terrorist activity. NorBAC determines that a plastic eating bacterium caused the blackout and they must stop it before more blackouts occur. David and Lilith's mother, rekindle old animosities when she comes to town to help Lilith deal with Mick's death. Caroline is worried about the possibility of having breast cancer. Bob Melnikov, NorBAC's Biochemist tells David he has been approached with another job offer.

Mayko Tran, NorBAC's bioinformatics researcher, notifies the team at NorBAC about a case of privately contracted civilians who have all returned from Iraq exhibiting a wide range of mysterious illnesses. Meanwhile, Carlos asks NorBAC to investigate multiple cases of hemophilia in a small community in Mexico, where a large multi-national laboratory is working on GMOs. Jill must defend her reputation as a top virologist when a research paper she published is refuted.

In the continued investigation of the "Iraq War Syndrome," David checks out a theory that the water purification system has malfunctioned. In Mexico, Jill and Carlos make a connection between a hybrid plant designed to detect land mines and the hemophilia epidemic. When that theory fails, David joins them in Mexico and explores the possibility that mosquitoes bred to eliminate malaria might be responsible. Bob quits NorBAC to pursue his love of perfume creation. Caroline receives the diagnosis she's been waiting for.

NorBAC has been taken over by a joint command to deal with a catastrophic smallpox scenario. Bob tries to find a cure for his dog that is suffering from histiocytosis. Jill comes clean with David about taking medication for her panic attacks. David discovers that the earlier "Miranda Virus" outbreak might be linked to the U.S. government's secret bio-chemical lab and that whoever manufactured the "Miranda Virus" may possess another, even more lethal, biological weapon.

David and Jill make a trip to Colorado where a rampant SARS-like outbreak is occurring. David is in shock when he discovers that the outbreak is Spanish Flu, the virus he dug up in Nunavut. Racked with guilt, he walks into the path of a car and is sent to hospital in a coma before he tells anybody his fears. Mayko Tran heads to Colorado to try to find Patient Zero.

Jill goes to Canada to see if the Spanish Flu body is still in the ground. David recovers from his coma and limps back to the office. Daisy recognises the person who created the Miranda virus and infected her baby. David identifies the vector for the Spanish Flu epidemic and tracks it with GPS.