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.

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.

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.

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.

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.

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.

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.

NorBac must find a cure to a bacterium that will surely kill David and Bob if they do not succeed. They also need to engineer the cure so that it eradicates the bacterium that was probably transported by the wind after the explosion of the lab in Utah.

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.

Mayko tries to get rid of the pain she's feeling in her phantom limb; the team investigates the high level of mercury contamination found in Lake McGraw.

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.

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.

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.

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.

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.

Several fires in British Columbia start. One of the action organizers calls NorBac in as several firefighters present strange symptoms. Craig, Rachel's son, come visit her mother at NorBac. Both Mayko and Carlos are attracted to him.

David ignores protocol and hires his new lover, Enuka; Mayko is contacted by the parents of a sick child who believe she's the only one that can help.

NorBac searches for the source of a resistant strain of c. difficile; despite his limited vision, Bob proves to be an asset to the team.

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.

What happened to Bob, Mayko, David, Jill and Caroline? 6 months after the explosion, NorBac is still rebuilding itself. The team has to deal with the deaths of several of their friends and colleagues and the arrivals of new people for the team.

It's a race against time to identify the cause of a deadly virus, spreading rapidly and headed straight for the city. It's up to NorBAC to identify patient zero and contain the outbreak. As if a deadly virus wasn't enough, NorBAC's Chief Scientist, David Sandström must deal with the unexpected arrival of his belligerent teenage daughter, Lilith, and arguments with NorBAC's Executive Director Caroline Morrison over the security clearance of the one member of his team he'll need the most, his top virologist.

Season 4 finale. A glimpse into the future renews David's determination to stop the birth of the first human clone.

NorBAC investigates a mysterious outbreak that is hospitalizing cyclists on the course of the Tour Cyclo Quebec. Meanwhile, Bob embarks on a controversial hyperbaric chamber treatment to deal with his brain infection and memory loss.

Carlos has disappeared for two days and David goes back to Mexico first to find Carlos and second help the Mexicans to fight the drug resistant TB that is killing tens of Mexicans in the region. Mayko and Rachel work non stop to find a cure to the TB and to find what is causing the inhabitants of Hudson Point, Illinois to be insensitive to pain.

A pharmaceutical company comes under fire when its newly-marketed immune suppressing drug triggers a high incidence of congestive heart failure; David attempts to find a replacement for Wes; Bob suffers a seizure that triggers romantic memories of a girl named Nina.

Bob continues to be haunted by memories of his time at Roth's secret lab; Wes insists that Rachel inject him with a highly experimental mutant red blood cells to fight the virulent Hep C; a mysterious disease that's causing brain inflammation in a small town appears to be contagious.

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.

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.

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.

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.

David discovers that NorBac has been tapped by Riddlemeyer. The team must find what caused the bear to attack Craig with no reason as a human being is presenting the same symptom. To save Bob's eyesight, David decide on a peculiar procedure.

David discovers that Roth has given the world's most powerful leaders the stem cell treatment that he now knows leads to violent paranoia; while investigating a mysterious outbreak in Moldova, Carlos uncovers a horrific act of atrocity.