The story takes place in the fictional Trumbull Valley. The first playable character is Marcus Campbell, a store clerk. After returning from a fishing trip with his friend and a Trumbull local, Ed Jones, he finds that the world has degenerated into a zombie apocalypse. The two are soon joined by Maya Torres, a soldier. They acquire a walkie-talkie and make contact with Lily Ritter. Following her direction, they make their way to a church called the Church of the Ascension, where Lily and several other survivors have made a home base. With Ed wounded, the trio accept Lily’s offer to let them stay.
As the game progresses, the survivors become aware of the United States Army’s presence in Trumbull Valley, led by Sergeant Erik Tan and Captain Diane Montressor. They soon learn that the army’s top priority is not to evacuate the survivors, but to contain and try to find the cause of the outbreak. The players also find the local civic leader — Judge Lawton — has barricaded the courthouse with the local law enforcement. She places citizens in her care under martial laws, planning to rebuild after the zombie incursion blows over. Finally, the players are also introduced to The Wilkersons, a group of hillbilly gun-runners who are using the apocalypse to profit and exploit other survivors.
Near the end, the courthouse falls to a zombie attack and Judge Lawton dies. Captain Montressor is evacuated, leaving behind Sergeant Tan and his men. The player, along with Tan, discovers numerous dead bodies dumped at the reservoir, explaining the cause of the infection. With long term survival no longer an option, they plan to leave the valley. After raiding a zombie-infested warehouse to get explosives, the group head to the only road leading out of the valley, now blocked with a massive concrete wall.
While Tan sets up the explosives, the player holds off incoming zombies. Tan realizes the detonator has malfunctioned, and the explosives cannot be detonated from a safe distance. He volunteers to manually detonate it, claiming he’s already infected. He sacrifices himself and sets off the explosives, which destroys the wall. As the smoke clears, the player sees the other side is also filled with destroyed cars and bodies, implying the apocalypse has already spread outside Trumbull Valley. The survivors leave the valley and the game ends.