Plot

In Ogden Marsh, Iowa, Dr. Judy Dutton finishes paperwork at the local hospital while her husband, Sheriff David Dutton, enjoys a local high school baseball game. Dutton’s deputy, Russell Clank, spots a man entering the outfield with a gun. David tries to get him to drop his weapon but is forced to shoot and kill the man. David and Judy begin to notice strange behavior in other town residents; they are slow to respond to questions and repetitive in their answers. The next night, a local farmer kills his family.

David and Russell investigate a dead soldier who is found in the woods and eventually find a crashed plane that has leaked a toxin into the water supply. Infected residents become extremely aggressive, attacking and killing other people. David tries to convince Judy to leave town but they are captured by soldiers and taken to a temporary military facility at the high school. Judy says that they are being checked for fevers and speculates the infection is a virus. An alert goes off when Judy is examined and she is taken away to be quarantined. She tries to explain that her fever is due to pregnancy, but is ignored and sedated. She wakes up strapped to a gurney as the perimeter of the facility is breached. The military personnel evacuates, leaving her and a room full of infected patients behind.

Meanwhile, David escapes from a group of people being released and rejoins Russell. The two go to the high school to rescue Judy and get there just in time to save her from an infected man who is killing the patients in their beds. The group begins walking out of town, hiding from both the infected and the military along the way. Eventually, Russell begins to show signs of infection and then sacrifices himself so that David and Judy can escape.

They arrive at a truck stop to collect supplies and hopefully find a working vehicle. They learn that the military also killed those who were not infected, taking no chances that the incident might be exposed. They survive another encounter with the infected and escape in a truck as Ogden Marsh is destroyed. David and Judy reach Cedar Rapids. A satellite view of the Earth shows the words “initiate containment protocol” as they are entering city limits.