
Unfortunately, the pilot soon became infected, forcing Zoey to shoot him, causing the helicopter to crash in an industrial district outside the city. Despite the opposition, they managed to reach the rooftop and contacted the pilot, who immediately made his way to the hospital rooftop and evacuated them as a Horde was attacking them. The group fought their way through Fairfield and reached the hospital, which was overrun with Infected. They manage to take down the incoming horde, which also included three new Infected strains just as a helicopter passed over the roof of the building they were in, informing any Survivors to make their way to Mercy Hospital for evacuation. Bill and Zoey discover a new Infected, which is immediately startled by Louis when he flashes his light at her, but they are able to kill her in time before she breaks the door down. Bill and Zoey soon hear crying and head to investigate the source, while Francis and Louis stand guard. Two weeks after the start of the epidemic, four immune individuals Bill, Zoey, Francis and Louis are in Fairfield, where Bill discovers the remains of an unusual Infected, signifying that they are evolving. Left 4 Dead begins in Pennsylvania, following an outbreak of the so-called Green Flu, a highly contagious virus whose symptoms include significantly increased aggression and the loss of many higher brain functions within its victim.

The Director keeps things from getting monotonous, however, by throwing in different challenges in every level. The basic gameplay never changes from map to map, so players will learn their way around fairly quickly. Infected players must cooperate to stop them. The goal of Left 4 Dead for the Survivors is to help each other make it through a level to safety. Regular Infected are controlled by the game AI, while human players can control up to four mutated Special Infected with special abilities in Versus mode. The game puts four human playable or AI-controlled Survivors of an apocalyptic pandemic against Hordes of the Infected. During early development, its working title was "Terror Strike."

The game was built using Source engine and is available on PC and Xbox 360. Left 4 Dead (abbreviated L4D) is a singleplayer and multiplayer cooperative survival horror FPS game developed by Valve Corporation and Turtle Rock Studios.
