When Season 1 ended David Sandstrom had gone on a self-imposed exile to China and the rest of the team are just about coping without him. However David is kidnapped by the PLA to investigate a recent outbreak that has killed 19 people in China. Later, David is horrified when he learns that one of the scientists has decided to test the antidote on her self in order to expedite a cure. While he makes his way back to Canada, a horrific protest by an individual ends up with him being shot dead and Audrey Graves, a pregnant woman who has been infected with a new strain of HIV from Africa by the protester via a needle.

With David back in the fold, the lab searches for a drug cocktail that can halt the progress of the new AIDS strain but it is too late to save the baby from contracting the virus. Meanwhile, Mayko recruits Simon Jessup, a British neuroscientist, to help her investigate a possible link between IQ spikes and Mad Cow disease. Mayko and Simon begin to develop a personal relationship before Mayko realizes that Simon is married.

While attending a conference in New York along with Bob, David’s meets up with Owen, a petty thief who leads him to an underground community where people are getting sick. Against his better judgment, David gets involved with finding out what makes them sick and is linked to the weed co-op run by the community. Owen comes to Toronto in search of David and ends up living with him for a while. Meanwhile, Jill believes that she has discovered a cure for juvenile diabetes from an unsanctioned line of Korean stem cells, while Caroline is distraught at the state of her nephew in a coma.

David & Carlos also investigate a bacteria that has  destroyed orange groves in Florida and they head to Cuba to trace the source. Back in Toronto, Caroline’s nephew Glenn fails to respond to his surgery, but does manage to utter one last, devastating message – he wants to die. The lab also investigates acidic rain clouds which is headed for Mexico City. Then Owen, who is a Meth addict, gets involved with a 16 year old girl who then dies after an overdose and he is charged. NorBAC must unravel a genetic mystery when fish bred in an East Coast fish farm start exhibiting unexpected and dangerous mutations.

On a personal note, David’s mother dies and he finds out that his father has Alzheimer’s disease and that he later burns down the family house. David has his father brought to a retirement home in Toronto. David is led to the work of a dead friend who was working on the gene that leads to homosexuality and was experimenting on mice. While working on a deadly virus that has affected a number of US soldiers, Jill is exposed to it and is hospitalized after she goes into a coma. David & Carlos use an authorized & experimental drug to keep her alive.

While they are working on the conspiracy by Caroline’s superiors and her assistant Wes is in on it, they are led to Connor McGuin, an ally of Caroline. Just as this all begins to sink it, a human bomb terrorist explodes in the lab. Who is killed, who will survive?