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.

As the search continues for the source of the deadly prions, NorBAC zeros in on a large agribusiness they suspect of selling infected chickens. David tries to convince Danny to stop gene therapy. Caroline insists that David interview Jill Langston, for the vacated virologist position at NorBAC. His reluctance turns to lust when he meets her.

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.