Plot
In the fictional town of Ogden Marsh, Iowa, resident Rory interrupts a local baseball game, entering the outfield with a shotgun. Sheriff David Dutten attempts to dissuade Rory but is forced to kill him when he raises his weapon. David's wife Judy, the community doctor, notices another resident, Bill, exhibiting bizarre behavior, including lifeless and repetitive speech. That night, Bill locks his wife and son inside their farmhouse and burns it down.
Following the discovery of a pilot's corpse in a swamp, David and his deputy Russell investigate the area. They discover a military aircraft that crashed into the river a few days before. Suspecting a link between the contaminated water and the residents' bizarre behavior, David urges Mayor Hobbs to shut off the town's drinking water supply. Hobbs refuses to authorize him, but David does so anyway. Responding to a disturbance at the morgue, David and Russell are attacked by the infected pathologist whom they kill with an electric saw.
Soon after, all communication services are cut off and soldiers arrive to quarantine all residents at the local high school. The residents are examined for symptoms of infection. Due to her pregnancy, Judy has an elevated temperature, is flagged as infected, and separated from David. Escaping quarantine, David returns to his office, encountering Russell. The pair head for the school to free Judy. At the school, the military personnel are unable to stop a large group of infected and evacuate, abandoning the site. Judy wakes up strapped to a gurney alongside several others. An infected Ben Sandborn enters with a pitchfork and begins killing the helpless people who are strapped to gurneys. David and Russell arrive in time to save Judy and Becca, her assistant.
The four make their way out of town on foot and witness soldiers killing Becca's boyfriend Scotty and his mother, then burn their bodies. David subdues a soldier and learns that the military has been ordered to shoot all civilians. They make it to David's house and begin fixing the patrol car in his garage. David is ambushed by Rory's infected wife Peggy and son Curt. David kills Peggy, and Russell shoots Curt through a window. Russell enters the room and shoots the pair's corpses multiple times, disturbing Judy.
David, Judy, Becca, and Russell flee in a car. On the road, they are spotted by an attack helicopter and drive into a car wash for cover. The infected carwash employees attack the car and drag Becca out by the neck with a hose, breaking her neck. When the rest of the group leaves the car to help Becca, the helicopter destroys the car.
While walking down the road, the group spots a black SUV speeding, which Russell disables with a police spike strip. The driver, a government employee, reveals that the cargo plane contained a Rhabdoviridae prototype and biological weapon called Trixie. It was en route to Texas to be destroyed when the plane crashed. Enraged, Russell shoots the driver and threatens the Duttens. David confronts him about his behavior, and Russell realizes he is infected. Russell begs to continue with them. At a military roadblock, Russell distracts the soldiers and tries to shoot at them but is killed. The Duttens sneak past and arrive at a truck stop to search for a vehicle, discovering that the military has also executed those who were evacuated. David also learns via radio that the military plans to destroy the town. After killing two infected hunters, they escape in a semi-truck. As they drive away, a massive explosion destroys Ogden Marsh and disables their truck, forcing them to continue on foot. A view from a military satellite highlights the couple and then the city, and the words "Initiate containment protocol" appear.
A semi-breaking up broadcast of a Cedar Rapids newscaster reports on the explosion in Ogden Marsh, stating a perimeter has been set and civilians are not being allowed into the area, then an infected's face unintentionally appears before the signal is lost.
