When a Congressman, a lobbyist and a Capitol police officer are stricken with a mysterious disease, Dr. Connor and his NIH team fear a terrorist plot, until the leader of a prostitution ring becomes the fourth victim. An uncovered list of "clients" turns up a "Who's Who" list of leading Washington figures, forcing the team to walk a fine line between politics and protocol to contain what seems to be a deadly STD. Meanwhile NIH Director, Dr. Ewing and Eva fight to keep the story out of the headlines. As the death toll increases and a blood test yields unexpected results, Connor's team must search for clues in the unlikeliest of places.

In the concluding half of the season finale, Dr. Connor and Frank are taken prisoner by rebels in a Central American country wracked by a meningitis outbreak and a deadly earthquake -- but the pair convinces the squad's leader (as Baracas, guest star Jesse Borrego) that his missing sons are trapped with Dr. McCabe in a ruined mission. As they work together and hope to arrive in time, Dr. Durant and Dr. Ewing fight a swelling meningitis epidemic that threatens a young mother and baby while much-needed supplies are hijacked. In addition, a sympathetic Eva can't ignore a forlorn boy who lost his parents in the temblor.