"Left 4 Dead" follows four survivors fighting a pathogen outbreak that transforms people into aggressive, mutated zombie hordes. The four survivors - Bill, Zoey, Francis and Louis - work together to fight the infected in hopes of finding evacuation to a safe place free of the outbreak.
"Left 4 Dead" is set in Pennsylvania. A highly contagious virus called Green Flu sweeps through the population, leaving only a rare few survivors alive who are immune to the virus. Bill, Zoey, Francis and Louis meet in Fairfield and set off together in search of Mercy Hospital after hearing of an evacuation point there. The group navigates through the streets, subway and sewers to reach the roof of the hospital. A helicopter picks them up at the roof, but the group discovers the virus is overtaking the pilot.
Zoey kills the infected pilot, and the helicopter crashes outside the city in an industrial district. They find a delivery truck and decide to head to the town of Riverside. The entire town of Riverside is infected, so the group gets a fishing boat to take them to Newburg. They discover Newburg burning and see a military aircraft pass above them that seems to be heading to the Metro International Airport. The group follows the plane and reaches the airport, only to discover that the military bombed it in an attempt to stop the spread of the infection.
The survivors escape in an aircraft they find on the runway, but end up crashing again. After a military quarantine efforts fails to capture them, they travel to Rayford and find a boat. Bill sacrifices himself and stays behind to power the generator and raise the bridge so the boat can get into the open water. The remaining three head to Florida.