Left 4 Dead is cooperative first person shooter set during a zombie apocalyptic pandemic in Pennsylvania. The game features four “Survivors” who fight their way through hordes of zombie infected in four game modes. There is a single player mode which teammates are controlled by AI; a four player co-operative campaign mode which plays the same as single player but with other people playing as survivors; an eight person Versus mode where players can play as the infected and try to stop the survivors from escaping; a four person survival mode where players face a continuous onslaught of zombies with the goal of seeing how long they can survive. In all game modes, the AI is controlled by the Director, who determines zombie hordes, level pacing and placement of game items in an attempt to create a dynamic experience and to increase the replay value of the game.
Left 4 Dead begins in a city of Pennsylvania, following an outbreak of a highly contagious virus called the “Green Flu”. The Green Flu causes loss of brain functions and highly increased aggression in humans turning them into violent zombies.
The game begins two weeks after the first infection with four immune survivors (Francis, Bill, Louis and Zoey) who must fight their way through the city of Fairfield. They discover the virus is mutating causing even more dangerous zombies than before. They fight past these newly special infected along with thousands of other zombie hordes. The survivors find out there is an evacuation point on the top of the nearby Mercy Hospital. A news helicopter flying above as alerted the survivors to meet at the hospital’s roof for extraction. Zoey, Francis, Bill and Louis fight their way through the city streets, sewers and subways and eventually to the top of the Mercy Hospital roof. They are rescued by the pilot only to discover he shortly later he was in contact with the virus. When the pilot turns infected, Zoey is forced to kill him, causing the helicopter to crash in the industrial district called Riverside outside the city. They find an armored delivery truck and the group decides to use this as their way out of town. While making their way out of town, the survivors come across a road block forcing them to exit the vehicle and travel the rest of the way on foot. The survivors eventually make way to a boat house where they hope to be rescued by a local fisherman. The fishing vessel drops them off on the other side of the river to the city of Newburg, which is engulfed in flames.
As the survivors rest inside a greenhouse, a large military C-130 Hercules airplane flies overhead. The survivors decide to make their way to the direction where the plane was flying, which was towards the city’s Metro International Airport. When the survivors arrive at the airport they see the military had bombed much of it, but the runway was still usable. Waiting for them is a C-130 airplane which the survivors are tasked with refueling before they can escape.
The Left 4 Dead survivors are once again stranded, this time in Allegheny National Forest outside the city. They follow a series of train tracks through the woods and head towards an abandoned military outpost. The survivors are contacted by the military through a radio transmission informing them to hold tight while a rescue vehicle comes for them. The survivors must defend a small farm house from relentless zombie hordes and special infected while a military APC arrives to take them to the last remaining safe zone in the Northeast.