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.

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.

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.