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.

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.

After a self-imposed exile to China, David Sandström is kidnapped by the People's Liberation Army and ordered to secretly investigate a deadly outbreak that has killed 19 people in a small village. With the help of three Chinese scientists, David discovers the outbreak has been caused by an ancient bacterium that has seeped into the village's water system. 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 David makes his way back to Canada, Caroline and Carlos are witness to a horrific attack at the site of the International AIDS Conference.

In order to help a mother and her unborn child, David starts a research to fight a very strong strain of the HIV virus which she has and for which there is no known cure.

The HIV strain that sean gave to Audrey Graves is so virulent that none of the new tri-therapy drugs work on it. They decide, then, to try a combination with any type of drugs that exist with the help of all the labs that accept the offer. Audrey Graves's baby is HIV positive and they hope to eradicate the virus with a new combination. Carlos is still searching for Patient Zero in Africa. In the mean time, NORBAC also looks at the devastating effects of pryon disease on humans via the consumption of infected chicken.

While in New York, David has his bag stolen. Chasing the kid who stole it, he finds himself in some subway tunnels where he discovers a young girl who is very sick.

Jill's new treatment for juvenile diabetes is halted when she discovers than the stem cells hold a retrovirus that might endanger the patients. The research on what plagues the girl found in the subway tunnel continues.

Carlos and David helped by a Cuban scientist called Eva Ramone look into a claim than an exiled Cuban is a victim of bio-terrorism. Bob being persuaded that Caroline's nephew, Glenn, is improving calls Simon Jessup to help him out.

David and Carlos are still investigating the poison that is affecting Charringa's lemon crops in Florida, before the United States decide to bomb Cuba. Jill, on the other hand, asks Mayko to contact all the other labs using the same stem cells from Korea to let them know a retrovirus is in that strain. Bob offers to verify all the steps one more time with her and see if her findings are correct. Simon Jessup finding that Glenn responds to all the stimuli suggests that he undergoes brain surgery.

Bob is trying to prevent a rain of concentrated sulfuric acid that would destroy Mexico City. Homeland Security suspects two American scientists of preparing a bio-terrorist attack against the United States President and order David and Caroline to investigate.

There is a series of suicides in Arkansas that Norbac is called to investigate. David tries to decipher the work of a friend who died in a car accident.

As the investigation continues on the suicides in Arkansas, the team believes it is a chemical release by worms that is the cause. Owen is charged with criminal negligence for the death by overdose of a school girl.

Despite David's public statement that GMO fish has no bearing on some illnesses, the dad of a young boy is convinced that his son is ill due to eating a the mutant fish. When an entire squadron of national guard falls ill, bio-terrorism is suspected, the team must work on the case.

It seems that the retrovirus that Jill discovered in the Korean stem cells is responsible for the illness affecting the national guards, thus showing the retrovirus was reactivated. Meanwhile, kids are all coming down with a mysterious and deadly disease that Norbac has to stop.

The antidote created to cure the national guards isn't doing its job properly as the guards fall even more ill with another disease. Caroline, still investigating what Weston did, finds that the White House is mixed into it.

The US government wants to cut over $3 billion out of the science budget, and NORBAC has to prove they deserve to stay in operation. Meanwhile, a West Nile like virus is breaking out in San Francisco, but it's showing some abnormal traits. A scientist at the University of Toronto claims to be able to help Owen with his addiction.