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.

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.

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.

Mayko finds the missing link to the Sinatra syndrome; Owen tries to commit suicide.

The team traces the Sinatra virus to an organ donor in the Philippines; David blames himself for allowing Owen to try experimental gene therapy to cure his drug addiction.

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.

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.

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.

A weaponized biological agent was released during fires on the west coast, NorBac must find the creator of the agent. However, Rachel is more worried about her son who was attacked by a bear.

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.

Bob undergoes his eye surgery in the hope he won't go totally blind in the process. Carlos and David are called in in a port in Nova Scotia where a ship's crew is missing except the captain who doesn't remember the past two weeks.

Fears arise that Carlos may have been infected with Crimean Congo Hemorrhagic Fever; after experimental surgery that improves his vision, Bob becomes hypersensitive to the emotions of others; Carlton comes under scrutiny when a magnetobacteria threatens the country's electronic infrastructure.

NorBAC discovers a link between the tantalum contamination and the recent smallpox scam; a viral activation of dormant genes evolves Bob into a higher consciousness.

Bob is back. His brain surgery caused an infection which leaves him in a bad shape when found. He is put into a medically-induced coma. The team travels to Mexico where an antibiotic-resistant strain of TB is killing the Zapatista Revolutionaries.

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.

As if being HIV positive wasn't enough, Wes is infected accidentally with a needle full of Hepatitis C.

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.

After an experimental treatment for Hep C nearly kills him, Wes quits NorBAC to enroll in a cutting edge HCV program in Stockholm; a racist city councilor claims his daughter was poisoned by Muslim extremists; the FDA is willing to fast-track some drugs in order to save an immune-deficient woman who was infected with smallpox.

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.

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 finally tracks down Nina, but on a visit back to Roth's lab he makes a gruesome discovery that suggests the experiment on Nina is about to go terribly wrong; the team investigates unusual crow attacks that appear to be targeting military airports.

A terrorist cell infiltrates the NorBAC lab and forces the scientists to produce a deadly measles mutation to be used as chemical warfare.

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.

When a young boy is murdered, forensic evidence leads the NorBAC team to investigate the unlikely existence of a prehistoric cat that disappeared from North America 10,000 years ago; a dramatic development complicates NorBAC's plans to deactivate Nina's Jacobson's organ.

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.

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