Plot

After a strange and insecure plane crash, an unusual toxic virus enters a quaint farming town. A young couple are quarantined, but they fight for survival along with help from a couple of people.

As a toxin begins to turn the residents of Ogden Marsh, Iowa into violent psychopaths, sheriff David Dutton tries to make sense of the situation while he, his wife, and two other unaffected townspeople band together in a fight for survival.—ahmetkozan

In Pierce County, Iowa; the sheriff is forced to kill the local Rory Hamill who suddenly threatens the community at a baseball game with a shotgun. The sheriff's wife Dr. Judy examines another local, Bill Farnum, who is also exhibiting a strange behavior. That night, Bill traps his wife and son in their home and then burns it to the ground, killing both. The following morning, the sheriff and his deputy are called by three hunters who have discovered a dead pilot in the nearby Hopman Bog. The sheriff and deputy find a large airplane at the bottom of the bog. The army suddenly seals off the town and imprisons the population in tents and concentration camps. The sheriff, his deputy, his wife and her medical assistant, escape. They quickly learn that the plane was airborne with a biological weapon and crashed into the bog contaminating the water supply of the population. To make matters worse, there is no antidote for the victims who are doomed to die or become incurably mad. The quartet tries to find a breach in the containment to reach the next town, but the escapees are hunted by the army.—Claudio Carvalho, Rio de Janeiro, Brazil

In the town of Ogden Marsh, Iowa, David (Timothy Olyphant), the local sheriff enjoys a baseball game. His deputy, Russell (Joe Anderson), spots Rory Hamill (Mike Hickman), a local resident, entering the outfield holding a shotgun. David is forced to shoot and kill the unresponsive Rory. David and his wife Judy (Radha Mitchell), the community doctor, begin to notice other town residents exhibiting bizarre behavior. The next night, a local farmer burns his house down with his wife and son trapped inside, killing them.

While investigating the discovery of a pilot's body in a swamp, David and Russell discover a cargo plane submerged under the water. Communication services are lost, and that evening soldiers wearing hazard materal suits arrive to take all residents to quarantine at the high school. Everyone is examined for symptoms of infection. Judy does not pass the examination and is separated from David. She explains her fever is due to pregnancy, but is sedated anyway. She wakes strapped to a gurney as the perimeter of the facility is breached by the infected. The military personnel evacuate, leaving Judy and others behind. David is nearing evacuation, but escapes and rejoins Russell. They rescue Judy and her medical assistant, Becca (Daniele Panabaker) from an infected citizen whom is killing those in the infirmery.

David, Judy, Russell, and Becca make their way out of town on foot, unable to find a working vehicle. They encounter Becca's boyfriend, Scotty McGregor (Justin Miles), when they pass through his farm. Soldiers raid the farm, shoot Scotty and his mother, and burn the bodies. The group repair a patrol car, and once on the road are spotted by an attack helicopter and drive into a car wash for cover. Infected car wash employees attack and kill Becca, and the helicopter destroys the car.

On foot, Russell disables a passing government SUV with a police spike strip. The driver, presumably a government agent (Glenn Morshower), reveals the cargo plane contained "Trixie," a "Rhabdoviridae prototype" biological weapon which has contaminated the water supply and is very contagious. Enraged, Russell shoots the driver and threatens Judy and David. When confronted about his behavior, Russell realizes he is infected and after being disarmed, begs to go on with Judy and David, later dying while distracting soldiers at a road blockade, so Judy and David can sneak past.

At nightfall, David and Judy arrive at a truck stop to search for a vehicle, discovering the military also executed all those who were evacuated from the town. Fending off three infected people who appear out of nowhere, they escape in a semitruck. Ogden Marsh is destroyed in a huge nuclear explosion as they flee, and their truck flips in the passing shockwave. As the couple walk towards Cedar Rapids, a view from a military satellite highlights the city, and the words "initiate containment protocol" appear, signifying another containment attempt since David and Judy are unknowngly infected by the Trixie virus.

In the closing credits, a news clip from Cedar Rapids Channel 9 is shown in which the newscaster (Bruce Aune) reports that a huge explosion originating from the Dakon Petrol chemical plant started a massive fire in Ogden Marsh, "with eyewitness reports of a 400-foot fireball that lit up the sky." He goes on to report a second explosion at a nearby truck fueling station, alluding to the truck stop. He says a perimeter has been set and civilians are not being allowed into the area. After that, the news clip cuts to a soldier with his rifle brandished, then to a snarling crazy, and finally simply the words "Signal Lost," strongly implying that the much larger city of Cedar Rapids was infected after the events of the film.