Games Source Left 4 Dead

Left 4 Dead


Left 4 Dead is a cooperative first-person shooter video game. It was developed by Turtle Rock Studios, which was purchased by Valve Corporation during development. The game uses Valve's proprietary Source engine, and is available for Windows, Xbox 360 and Mac OS X.


Left 4 Dead begins in Pennsylvania, following an outbreak of so-called "Green Flu", a highly contagious virus causing extreme aggression and loss of higher brain functions.

Two weeks after the infection of Patient Zero, four immune survivors of the outbreak (Francis, Zoey, Bill, and Louis) make their way through the city of Fairfield, only to discover that the virus is creating new, even more dangerous mutations. After narrowly avoiding these new infected, along with hordes of others, the survivors are alerted to the presence of an evacuation point at the nearby Mercy Hospital by a passing news helicopter. Fighting their way through the city's streets, subway and sewers, the survivors are rescued from the hospital's roof by the pilot, only to discover that he is succumbing to the infection. ("No Mercy") With Zoey forced to kill the pilot, the helicopter crash lands in an industrial district outside the city. Finding a delivery truck that has been armored by other survivors, the group decides to use it to make their way to the town of Riverside ("Crash Course"). Before arriving in the town however, they find the road blocked, and are forced to travel the rest of the way on foot. Following an encounter with an infected madman in the local church, they discover that the town is overrun, and decide to head to a nearby boathouse for possible rescue. Contacting a small fishing vessel, they manage to reach the city of Newburg on the other side of the river, only to find much of it in flames ("Death Toll").

Seeking cover in a large greenhouse, their rest is interrupted when a military C-130 Hercules passes overhead, leading the survivors to travel through the city's business district towards Metro International Airport. Upon arrival, the group is shocked to see that in an attempt to contain the infection, the military had bombed the airport; the runway however is largely intact, allowing the survivors to fuel up and escape in the waiting C-130 ("Dead Air"). Despite this apparent rescue, a second crash occurs, and the survivors once again find themselves alone on the outskirts of Allegheny National Forest. Following a series of train tracks through the area, the group find themselves at a functioning, but abandoned, military outpost. After answering a radio transmission, the survivors make their final stand against hordes of infected, before a military APC arrives to transport them to Northeast Safe Zone, supposedly the only location in the area yet to be overrun ("Blood Harvest"). They are temporarily held by the military before the base is overrun with infected. The four escape via train and travel south at Bill's insistence; Bill believes that they can find long-term safety from the infected on the islands of the Florida Keys. (The Sacrifice comic) At the portside town of Rayford, they find a boat but must raise an old rusty bridge powered by an aging generator to get the boat into open waters, assured that the machinery noise will alert a large horde. When Louis is injured and unable to move quickly, Bill sacrifices himself against the horde to make sure the generator keeps running and allowing the three to stay clear of the horde.("The Sacrifice") After waiting for the horde to disperse, the three are taking time to mourn Bill's death when they encounter the four survivors from Left 4 Dead 2, who need to cross the bridge to continue to the west. ("The Passing") Zoey, Louis, and Francis help the four to get across and fend off another horde as they lower the bridge, and then set sail for the Keys.


Left 4 Dead is a first-person shooter. In campaign mode, the player takes control of one of the survivors; if four human players are not available, then the remaining survivors are AI-controlled bots. They play through the levels fighting off the infected—living humans who have been infected with a rabies-like virus that causes psychosis, to which the survivors are immune.

The game is focused on cooperation and team play and thus eschews some "realism" conventions usual in most FPS games of the wider genre; colored outlines of teammates are visible through walls to help players stick together and coordinate their movement. If a survivor falls off a ledge, then they may automatically hang onto it and can only be helped up by another survivor. If a survivor's health is depleted, then they become incapacitated and can only be revived by another survivor, at which point they continue playing with a low amount of health that decreases over time. If a survivor has been incapacitated and revived twice without tending to their wounds, then they will experience distorted black-and-white vision, and the next incapacitation will kill the character. If a survivor takes enough damage while incapacitated, or is not eventually helped up by teammates, then the incapacitated character will die. During "Campaign" mode, if a survivor is killed, then they will respawn in a closet or other enclosed space after a period of time (except during key points in the scenario), but must be freed by another survivor to rejoin the team. Otherwise, the player must wait until the next level. However, if all human player survivors are killed or incapacitated, players will have to restart from the last checkpoint. Survivors can share first-aid kits and pain pills and help each other heal. Left 4 Dead has friendly fire that cannot be disabled, increasing the need for caution around other survivors. On the easy difficulty level, friendly fire does not harm teammates but still registers as having occurred with a notice on the screen saying, "Don't shoot teammates!"

The survivors communicate by voice commands that are accessed by quick menus, and some may sound off automatically when performing actions such as reloading or spotting infected. Over 1,000 unique lines have been recorded for each survivor. Additional communication of player actions is conveyed through character lights. Also, weapon-mounted flashlights and muzzle flashes help the players in determining whether their companions are shooting, performing melee attacks, reloading or moving. Due to control issues and the likelihood of players using a LIVE headset, the Xbox 360 version of Left 4 Dead omits the quick phrases feature.

The game is experienced through five campaigns that take place in various urban and rural locales. Multiple visual in-game hints—including license plates, park signs, markings on airport equipment, and lines of dialogue spoken by the survivors—suggest that these locations are in Pennsylvania, and similarly a memorial wall giving names of those who have died in the infection (actually names of the game's development team) along with their dates of birth and death suggests that the game takes place in October 2009. Each campaign is divided into five chapters (except Crash Course, which has two chapters) marked by safe rooms, which are checkpoints where players can heal, re-arm and revive characters who were killed. Specifically, the four campaigns are: "No Mercy", an urban setting culminating in a hospital skyscraper; "Death Toll", a small-town and countryside setting; "Dead Air", an airport setting; and "Blood Harvest", a woodland and farm setting. A two-level campaign, "Crash Course", was released on September 29, and is set in the outskirts of a small industrial town. The levels have distinct beginnings and ends, but there are a number of alternate routes to follow with more supplies, helping to create a sense of non-linearity. In the final chapter of each campaign, the players must defend a position from an onslaught of infected until rescue arrives. Each campaign typically lasts between 20 and 75 minutes depending on the difficulty level. Both platform versions of the game utilize an achievement system.

Survivor characters

There are four playable human characters in the game: Francis, a stereotypical biker (voiced by Vince Valenzuela); Bill, a Vietnam Veteran (voiced by Jim French); Zoey, a university student (voiced by Jen Taylor); and Louis, a district Account Manager (voiced by Earl Alexander). Louis' profession is now listed as a Junior Systems Analyst in the IT department for Franklin Brothers in Philadelphia, keeping in line with the comic released for "The Sacrifice" DLC. Early plans were for players to be randomly assigned to characters but in the final release, players can choose any character—provided that the character has not already been selected—or be randomly assigned an unselected character. Aside from appearances, all of the characters have identical abilities in-game.


Survivors are armed with various firearms. Each player starts the game with an M1911 pistol. It may be reloaded an unlimited number of times and is the only weapon that the survivor can use when they are incapacitated. When a second pistol is found, the player can dual wield them. At the beginning of each campaign, the player can choose between an Uzi submachine gun and a pump-action shotgun. As the survivors progress through a campaign, more powerful weapons can be found: the fully automatic M16A3 assault rifle (an upgrade to the Uzi), Benelli M4 Super 90 semi-automatic shotgun (an upgrade to the pump-action shotgun), and a scoped Ruger Mini-14 hunting rifle. A flashlight that can be toggled on and off is mounted on each firearm, with the exception of additional pistols. In addition to firearms, a player can also carry three other items in their inventory: improvised grenades (either a Molotov cocktail or a pipe bomb modified with an attached smoke alarm designed to attract the infected to it before it explodes); a first aid kit, which can be used to heal any survivor and pain pills, which provide temporary health that depletes gradually and quicker with damage from infected, and can be handed to teammates for later use. Regardless of what weapon or item a player is using, a melee attack can be used to shove away any infected within reach in Left 4 Dead 2. Also available are environmental weapons, such as gas cans, propane cylinders, and oxygen tanks, all of which explode when shot. These environmental weapons can be picked up, moved, and used as a melee weapon by the survivors, but while carrying an object they cannot use their weapons or health items. Strategically-placed minigun turrets are also encountered at various locations throughout the different maps.

Infected characters

never seen eating human flesh or brains, multiple 'survivors' who have been killed by the infected appear throughout the game, and appear to have been partially eaten. In The Sacrifice comic, Zoey's mother is bitten in the face. She then begins to attack the rest of her family. One such victim can be heard saying "I can't believe he bit me!" before being encountered later on, fully infected. In an interview with, Mike Booth commented on the concept of using a pathogen as an inspiration for the setting:

“Even though we obviously pushed well beyond the realm of believability with many of our "boss" infected, the core idea of a mind-destroying, civilization-collapsing pathogen is more horrifying to me than magically animated corpses, precisely because it is plausible. Rabies is a good example of a pathogen that can turn a loyal, friendly, protective family pet into a slavering attack machine. It is a virus that reprograms the behaviors of a complex animal – a mammal, in fact. What if something similar happened to humans? Left 4 Dead is one possible answer.”

The common infected encountered during the game are fast and agile, weak individually, but may be overwhelming in numbers. They display a special attraction to high-pitched alarm-type sounds, such as the beeping device attached to pipe bombs and car alarms. Common infected will often chase down the source of these noises while ignoring lower-pitched, but much louder sounds such as gunfire. They occasionally attack in masses referred to in-game as a "horde".

In addition to the common infected, there are five "special" or "boss" infected whose mutations grant them special attacks that make them far more dangerous. Each of the special infected, as well as approaching hordes, have a distinctive sound or a timely musical cue, making their presence easily recognizable by players. There are five special infected in Left 4 Dead.

The Boomer is a bloated infected that can spit vision-impairing bile on the Survivors that attract hordes of infected, and explodes on death, spewing more bile in the immediate area.

The Hunter is an agile foe that can jump and pounce on a Survivor, and then tear at his victim until he is knocked off, kills his prey or is killed.
The Smoker is a horribly deformed zombie, with its right arm completely covered in boils, and the right side of its face swollen and blistered. The smoker has a long tongue that it uses to ensnare and drag a Survivor back to himself. It will then either attack the Survivor directly, allow the horde to attack him, or leave the Survivor suspended over a cliff or roof-edge; the Smoker only releases its victim once the tongue is shot, the Survivor is killed, or upon the Smoker's death, which results in an explosion that leaves a vision-blinding cloud lasting approximately 30 seconds.

The Tank is a gigantic muscular infected that has the ability to swipe at Survivors, knocking them off their feet and incapacitating them; it can also knock cars and other debris into the Survivors.

The Witch is a passive female infected that stays in a spot, crying; Survivors can sneak by the Witch, but if they disturb her with light or loud noises, she will become aggressive and attack the Survivor that alerted her, usually incapacitating the Survivor and attacking him until she or the Survivor is killed, except when playing on Expert difficulty, where she kills the Survivor instantly. It is also possible to kill the Witch before she even has a chance to get up; this can with one auto-shotgun hit directly to the Witch's head at point-blank range.

Each of these special infected is preluded to players through special audio cues. The Witch's cries, the Hunter's growls, the Boomer's gurgling, and the Smoker's coughs can be heard before they are seen, while certain musical cues will alert the players to the presence of a Tank in the area. Along with the special infected, there is also a special musical cue for whenever a horde is coming.

One special infected did not make it into the game. The "Screamer" was an infected strapped in a straitjacket and let out a loud, high-pitched scream when it sighted the survivors, thus forcing the survivors to find and kill it before it screamed, resulting in a horde of common infected. However, it ended up being too difficult for players to figure out where the Screamer came from or where it was going or even understand that they were meant to chase it. Because of the confusion, it was replaced by the Boomer.

In versus mode, four additional players can take control of the special infected—apart from the witch, who remains computer-controlled. Each infected player is randomly assigned a class of special infected when they enter a spawn mode. While in spawn mode, the infected can quickly roam around the map in search of an appropriate place in which to spawn. This location must be sufficiently distant from any survivor, out of the line of sight of any survivor, and outside restricted areas such as safe rooms. Upon death, the infected player must wait up to 10–25 seconds before reentering spawn mode, depending on how many players are on the infected team. When a tank is spawned in the game, infected players receive a message indicating which player will control it. The human-controlled infected can see their teammates' outlines through walls similar to the survivors, but can also see each survivor's outline, which is colored according to the survivor's health and fades out if the survivor refrains from attacking, running and vocalizing. Vertical pathways exclusive to the infected, such as pipes and vines, are marked with animated symbols for the infected players. These can be climbed and used for ambushes.

AI Director

The artificial intelligence of Left 4 Dead features a dynamic system for game dramatics, pacing and difficulty called the "Director". Instead of fixed spawn points for enemies, the Director places enemies and items in varying positions and quantities based upon each player's current situation, status, skill and location, creating a new experience for each playthrough. The Director also creates mood and tension with emotional cues, such as visual effects, dynamic music, and character communication.

Valve has termed this dynamic set-up "procedural narrative". In addition to the AI Director, there is a second Director that controls music. It was created as a way to keep the music interesting throughout the game. The music Director monitors what a player has experienced to create an appropriate mix. The process is client-side and done by a multi-track system. Each player hears their own mix, which is being generated as they play through the game, and dead players watching a teammate hear their teammates' mix.

A far simpler version of the A.I. Director was previously used for some key battles in Half-Life 2: Episode Two.

Valve is looking for ways to apply the Director in their future games to make pacing and difficulty more dynamic.

Game modes

Left 4 Dead contains four game modes: campaign, versus, survival, and single-player. The cooperative campaign consists of up to four human-controlled survivors who attempt to make their way between safe rooms and eventually to rescue. In this mode, the special infected are controlled by the AI. In a versus campaign, each team of one to four players plays each chapter of the campaign as both survivor and infected, swapping sides once per chapter. Unlike campaign mode, dead survivors do not respawn. If at least one player-controlled survivor finishes the level, the survivor team earns 100 points as well as bonus points based on their health and the health items in their inventory. These points are then multiplied by the chapter's difficulty level, and the number of survivors who finished. If all player-controlled survivors are killed, the survivor team only earns points according to their average progress through the chapter and the difficulty multiplier. Survival mode consists of a timed challenge where players try to survive as long as possible against a never-ending flood of the infected, added in April 2009 in the Survival Pack downloadable content. Single-player mode is basically the same as campaign mode, but played offline with three AI-controlled bots as the other survivors. On Xbox 360, other players can join in on the same console to turn single player into an offline co-op game. The game can also be played through a system link, or local area network. Players have also discovered a way to do splitscreen co-op play with the PC version.

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