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.

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.