The player can choose from several locations to build a base, then reinforce and improve it with various facilities like watch towers, gardens, sleeping quarters, kitchens, workshops, medical bays, etc. to help keep survivors safe and healthy. Part of the game is balancing the use of resources: food, medicine, ammo, and construction materials. They can be obtained by scavenging, trading with NPCs, only food can be grown at the base.
The player can interact with survivors outside of their group: trading with them, helping them or recruiting them. The game features two relationship meters, the first determines if a survivor can be recruited, and the second dictates if they can be controlled. Only one survivor can be controlled at a time, though the player can ask an AI-controlled survivor to accompany them, and in certain missions, one or more AI-controlled survivors will accompany the player.
The Storyline mode features around 150 characters, with varying facial features and clothing. Each character has a fixed set of “traits” which give them advantages or flaws (such as tire out more easily, or can improve a certain skill faster). Except for the story-related characters, most characters can be assigned to survivor groups and be recruited. Each character also have an “attitude” parameter, affected by game events (a near death experience, death of another character, or having accomplished a difficult task). These attitudes can affect their behaviors, sometimes requiring player intervention.
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.