Set in a modern day survival-horror universe, the co-operative gameplay of L4D casts four “Survivors” in an epic struggle against hordes of swarming zombies and terrifying “Boss Infected” mutants. The Survivor Co-op Game Mode is played out across four sprawling campaigns, set in urban and rural environments. Each campaign has an over-riding team objective, and is comprised of five large maps. The campaigns link together to tell the story of the Survivor’s escape to safety. The team of four Survivors may be comprised of 1 to 4 human players, allowing for single player and multiplayer co-op games.