Dr. Stephen Connor conflicted with his job's demands and challenges and his role as a newly separated father with a young son. Connor and his team are called into action when a puzzling illness begins to turn people blue, while McCabe, eager to impress Connor, is called in to help solve what appears to be a case of child abuse.
The NIH team searches for the source of encephalitis that has infected a group of teenage girls in St. Louis.
When four war veterans die of similar causes, the initial assumption is that is a form of post-traumatic shock, but then it's revealed that the disease is actually related to an old age home.
Part of the medical investigation team quarantines a vacation spot when guests start dying while two stay behind to discover the cause of illness behind people tied to an art gallery.
When about a dozen children start to come down with serious muscle inflammation and joint pain, the initial assessment leads to a nearby chemical plant but it's discovered that the children were all conceived in virto as well and share the same DNA.
College football players and then sorority sisters start to fall ill with an unknown nerve disease. The NIH team is on the clock as they have to discern the origin before crowds of people start pouring in for the homecoming game festivities.
A bride-to-be takes ill at her bridal shower and is soon joined by others as the NIH team rushes to find the source of a possible anthrax outbreak before a newspaper can send the entire city of Philadelphia into a panic.
One out of ten residents of a West Virginia town die due to a mutating virus and the NIH team races to discern the source and treatment.
A little girl is one of the first people to show signs of aplastic anemia in a town, but while the search is on for a compatible bone-marrow donor, others start to manifest.
When stars of adult films start to fall prey to an illness, the team suspects an STD but when a case appears in suburbia, they widen their net to try and out the source.
The team must root out the source of a flesh-disease running rampant through a Maryland hospital.
Dr. Connor and his team try to link the deaths of seals to the illness that starts to infest a seaside California town.
A family comes down with a skin rash and a fever that turns out to be smallpox. Connor and Durant treat them and then find out another family has also been infected. An investigation leads them to discover a scientist who may have unleashed the virus on purpose.
Powell falls prey to a dementia the team is sent to investigate at an Arctic research station.
Dr. Connor's team tries to track down the source of a deadly plague that's infected police officers, a fugitive and two children. The search leads to a murder victim and heroin shipments.
Connor splits the medical investigation team to deal with two separate calls. Miles looks into miscarriages occuring at a military base. Durant and Connor look into paralysis suffered by people who were near the horrific events of 9/11.
Connor and team work to save the life of Third Watch paramedic Carlos Nieto even as Yokas tries to help them track down the robber and source of the disease. Holly gets consolation from Eva as the threat of death looms over her boyfriend.
When important political figures start to fall to some unknown illness, the initial fear is a terrorist attack. It appears that the only link is a Washington madame and Connor must fight against bureaucracy and politics as well as the disease.
When Connor and his team go to an unstable country to help against a deadly disease, war and an earthquake undermine their ability, especially after the three men are taken hostage.
Frank and Connor, work to save their captor's sons who are trapped in ruins with McCabe. Durant and Ewing try to tackle the meningitis outbreak. Eva tends to a boy who lost his parents to the earthquake.