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wielding his trademark crowbar in front of the Blast Pit Tentacles, while a pair of security guards fall to their deaths in the background.
This article describes the Half-Life storyline as it is played in-game; chapter by chapter.
 Hazard Course (optional)
This chapter is the training chapter of Half-Life, and takes place in the Black Mesa Hazard Course in the Training Facility. It trains the player to use the HEV Suit, how to move around within the environment and interact with it, how to use weapons and how to use the Long Jump Module. Scientists observe as Gordon trains and dodges environmental hazards.
- In Opposing Force, the player can visit the Hazard Course at the duck-jump training room by using the Displacer Cannon in Xen, where Adrian Shephard first acquires it. The room appears to still be functioning, as the Hologram and success markers still function. A nearby Vortigaunt mistakes the Hologram for a real person, attacking it. It soon realizes that the Hologram is fake, and proceeds to attack the player.
- In Half-Life: Decay, one of the chapters happens to be Hazardous Course, in which Doctors Colette Green and Gina Cross walk through the destroyed remains of the course. The Hologram in the course is Gina Cross, one of the main characters in Decay.
 Chapter 1: Black Mesa Inbound
This is the first chapter of Half-Life. It serves as the introduction to the game and follows the player character, Gordon Freeman, as he rides a train through the facility to Sector C. The public announcement system introduces the facility to the player.
Gordon Freeman rides a tram deep into the heart of the Black Mesa Research Facility on his way to the Anomalous Materials Lab to begin work. Nothing seems to be out of place, except a chemical leak that forces the tram to momentarily stop. A strange man in a blue suit is seen watching Gordon from another tram, who is later known to be the G-Man.
- This chapter features the only confirmed sighting of Barney Calhoun in Half-Life, affirmed by the beginning sequence to Half-Life: Blue Shift.
- When viewing the penultimate map of this chapter in an external map viewer it's possible to see a different version of the Sector C Test Labs entrance behind the door. This is also achievable through the use of cheats.
 Chapter 2: Anomalous Materials
- "They are waiting for you Gordon... in the Test Chamber"
- ―A scientist reminds Gordon of his duty
This chapter follows Gordon Freeman as he arrives at the Anomalous Materials Laboratory in Sector C, dons his HEV Suit, and participates in a mysterious experiment in the test chamber.
Later on, once he reaches his destination, Gordon glimpses the G-Man arguing heatedly with a scientist behind soundproof glass. After donning his HEV Suit, he proceeds to the test chamber, containing a large anti-mass spectrometer. Immediately after pushing an alien sample into the scanning beam, the system goes critical, triggering a Resonance Cascade. This opens an inter-dimensional portal between Earth and a bizarre alien world known as Xen. Gordon is briefly teleported there during the ordeal, at one point encountering what appear to be sentient life forms, including Vortigaunts. Gordon blacks out shortly after.
- At the beginning of the chapter, behind the desk where the security guard is sitting, there is a red and green switch. If used, it will momentarily set off an alarm.
- In the same room the security guard is sitting, there is a small set of machinery in the lower left corner. There is a red and a green button on the front of it. Upon pressing the use key on either of them (they are part of the same model), a laptop folds out on top of the set of machinery. The owner of the laptop, a scientist, sees this and scolds the player, saying he's "expecting a very important message" and closes the laptop and locks it preventing Gordon from using it.
- In Gordon Freeman's locker can be found several easter eggs: a baby's picture and the books The Orchid Eater and The 37th Mandela, written by the series' writer Marc Laidlaw. Other lockers bear the names of Valve employees, such as Marc Laidlaw, Kelly Bailey, Ted Backman, Chuck Jones, John Guthrie (which is open in Unforeseen Consequences and contains an American flag and ammo for the pistol), Ken Birdwell, etc.
- In the test chamber, if the sample is pulled from the Spectrometer, one of the Vortigaunts teleporting in there won't teleport out; instead, he stands on the cart and attacks Gordon. He will be there after the map change, floating in the air, therefore it is not advised to remove the sample.
- If, by using the "impulse 101" cheat, you fire the Hivehand weapon into the pit of the Anti-Mass Spectrometer in the test chamber, it will cause the resonance cascade without having to activate the machine or push the specimen into place.
 Chapter 3: Unforeseen Consequences
Headcrab in the Ionization Chambers room after the Resonance Cascade.
This chapter details Gordon Freeman's efforts to reach the surface to get help in the aftermath of the Resonance Cascade. This chapter introduces the player to weapons, combat and environmental hazards, among other things.
The title alludes to the G-Man's words to Eli Vance prior to the Resonance Cascade, where he told him to "prepare for unforeseen consequences". As revealed by Eli to Gordon in Half-Life 2: Episode Two, the G-Man is who gave him the sample.
Waking up back in Black Mesa, Gordon makes his way out of the test chamber. Gordon manages to reach his colleague, Eli Vance, who informs him that all communication outside Black Mesa has been lost. Eli requests that Gordon try to reach the surface in order to find help. Black Mesa has suffered massive structural damage, and aliens from Xen begin randomly teleporting all around the facility. Most are simply reacting naturally to their new surroundings, but even more hostile are the creatures glimpsed earlier, known as Vortigaunts, who seem to attack with a single-minded intent to kill. Gordon also occasionally witnesses the G-Man, watching him from out-of-reach places.
Since the tram is too damaged to work, Gordon must cross Sector B's Coolant Reserve Facility in order to find a way out.
- After exiting the test chamber, a scientist resuscitating a security guard can be seen. He eventually regains consciousness if the player waits long enough.
- The door leading to the monorail can be opened after the Resonance Cascade by destroying its monitor (or the controller). Through the door a scientist can be found, who will fall to his death. Ammo can also be found there.
- The title alludes to the G-Man's words to Eli Vance prior to the Resonance Cascade, where he told him to "prepare for unforeseen consequences". As revealed by Eli to Gordon in Half-Life 2: Episode Two, the G-Man is where he got the alien sample from.
- This chapter introduces the most iconic weapon of the Half-Life series - the Crowbar.
 Chapter 4: Office Complex
Two Headcrabs approach Gordon.
Gordon makes his way to the office complex, where several scientists are barricaded in their rooms, hiding from the rampant aliens appearing inside the complex. Gordon overhears rumors from these scientists that the military has arrived to rescue the people trapped in the facility. Gordon proceeds on his journey to the surface.
The Freezer area can be skipped. A security guard can be found prior to the area; if he is taken to the door on the left of the entrance to the freezer and then pushed into it, he will get stuck in it for a while and the door will open, allowing for progress.
 Chapter 5: "We've Got Hostiles"
Gordon engages the HECU in combat.
This chapter finds Gordon passing through various storage and staging areas, continuing his hunt for a way to the surface. Gordon learns that the soldiers rumored to be coming on a rescue mission have already arrived. While attempting to join up with them, Gordon witness a Marine killing an innocent scientist, realizing that the Hazardous Environment Combat Unit, which has taken control of Black Mesa, is not just killing the aliens, but are killing everyone connected to the project.
Gordon proceeds on his journey, fighting his way through both aliens and marines. He eventually reaches the surface, finding himself in an area totally under the control of the military, and in the middle of an artillery bombardment, which forces him to retreat back into the underground complex. Back underground, Gordon learns from a scientist that the surviving members of the Lambda Team, in the Lambda Complex at the other end of the facility, may be able to close the dimensional rift. Gordon starts a trek across Black Mesa to reach them.
In the beginning of the chapter, a scientist is seen screaming about opening the silo doors. You can crowbar him once, and he can run into the door to the office. In the office (where the zombie drags the guard into the air vent) you can press the button to open the silo door, and continue to Blast Pit, without needing to complete the entire level.
 Chapter 6: Blast Pit
Tentacles in the blast pit.
Gordon Freeman enters an abandoned, largely sealed-off area of Black Mesa, dating back to its earlier days as a missile complex. The area is full of mothballed machinery, and is now used as a dumping ground for toxic waste from the rest of the facility. The HECU soldiers lack a foothold in this area of the facility due to the high concentration of aliens present. Here, Gordon encounters a deadly new foe, the Tentacle. After reactivating the fuel, power, and oxygen lines, Gordon manages to incinerate the Tentacle by activating the rocket engine at the top of the silo that the Tentacles were inhabiting, and finds a way out through the meters-long dirt tunnel dug by the Tentacles.
- The old level name featured on Half-Life: Day One, given in the "titles.txt" file was: Screams and whispers.
- The Scientist taken by the Tentacle can be saved; by running to the scientist and talking to him as soon he begins to run. The scientist will talk without being taken by the Tentacle. The Tentacle will do its scripted movement.
- In one part of the chapter, Gordon needs to get in the vent at the ceiling high above him. He does this by turning on the fan, which makes its blades to constantly move. After this, he jumps in the moving air above the fan. While this "flying" is possible in the real world it should be noted that the wooden planks near the vent, fall straight down, which is in contradiction to Gordon's state.
- After killing the Tentacles and going down the tunnel, if the player is to return back (by means of noclipping) then the Tentacles will reappear as they weren't killed. This may not happen in the Steam version.
 Chapter 7: Power Up
Two HECU soldiers fighting the Gargantua.
Trying to reach the surface once more, Gordon's progress is thwarted by a clash between a Gargantua and HECU soldiers in the Sector E Materials Transport. He learns from a dying security guard that if he restores the generator, he can ride the monorail to the surface. Freeman enters the Houndeye-infested subterranean areas and activates the generator, restoring power to the vicinity. After activating more switches, he destroys the Gargantua patrolling the area by turning on the huge transformers supplying power to the tram line.
Boarding a monorail, Gordon smashes through a barricade of concrete blocks before proceeding on his way.
- The old level name featured on Half-Life: Day One, given in the "titles.txt" file was: Footfall.
- If the player attacks the dying security guard, he'll say the lines that the others do when attacked, but stay lying down.
- The entire level can be skipped by proceeding to the railway barricade, then using tripmines as steps to climb over the barricade.
 Chapter 8: On A Rail
As Gordon Freeman rides the monorail through the Materials Transport section of Black Mesa, he learns from a security guard that he must ride to the High Altitude Launch Center to launch a satellite, which the Lambda Team can use to reverse the effects of the Resonance Cascade. Gordon encounters further resistance from the HECU forces, now actively hunting him personally, in revenge for the large number of marines he killed on the way. Gordon eventually makes his way back up to the surface again, through use of several elevators, and makes his way to the launch site. At the launch site, he sends the rocket up into orbit, but is once again forced to go back underground.
 Chapter 9: Apprehension
Gordon under attack by a Vortigaunt.
Continuing towards the surface, Gordon encounters a deadly new aquatic enemy, the Ichthyosaur, and acquires a crossbow. After an underwater battle with the creature, he manages to escape and continue on his way.
After battling the Black Ops, another "rescue" crew trying to kill even the HECU marines, Freeman is ambushed and captured by two marines. They remove all of his weapons, and leave him unconscious in a trash compactor.
The old level name featured on Half-Life: Day One, given in the "titles.txt" file was: Abandoned silo.
 Chapter 10: Residue Processing
Gordon continues to fight his way through and outside the facility.
One of the several hazardous material tanks to come across.
Gordon wakes up, and manages to escape from the trash compactor. While once again heading back to the surface, Gordon stumbles across a mostly abandoned part of the facility, meant for processing and disposing of waste and hazardous materials. Making his way through antiquated compaction machines, great vats of waste, and furnaces, as well as riding on gravity-defying conveyor belts, Freeman escapes to a hidden part of the facility.
The old level name featured on Half-Life: Day One, given in the "titles.txt" file was: Chutes and ladders.
 Chapter 11: Questionable Ethics
Gordon Freeman facing several Houndeyes, shortly before discovering captured Alien Grunts and Headcrabs.
Gordon finds himself in a secret part of the Black Mesa facility, where he discovers that scientists had been "collecting" specimens from the parallel universe Xen long before the resonance cascade occurred.
Gordon Freeman continues to rearm himself against the HECU, and fights his way through them, as well as various alien enemies. Gordon encounters for the first time the alien military units, the Alien Grunts, and manages to scavenge a powerful experimental weapon, the Tau Cannon, from the remains of a scientist and security guard. He proceeds on his search for the Lambda Complex.
 Chapter 12: Surface Tension
View of the canyon from the cliff where a HECU soldier is waiting for Freeman.
After arming himself with advanced prototype weaponry, Gordon again reaches the surface, which has become a war zone. The Vortigaunts, along with Alien Grunts and Gargantuas, have begun making determined attacks against the Marines, and the tide of the battle begins to turn in favor of the aliens. Gordon scales a cliff wall and navigates several bombed out buildings, while combating both sides, as the forces of Xen begin to dominate the battlefield. Finally, Gordon reaches relative safety underground.
- The original name of this chapter, Cliff Hanger, was used on E3 1998.
- Like "Half-Life", "Blue Shift", "Opposing Force" and "Decay", "Surface Tension" is a scientific pun, referring to the properties of water which makes certain objects float above it.
- A part of a map in this chapter was used to create the map Hunted in Team Fortress Classic.
- The canyon scene was mirrored at the end of the Half-Life 2 chapter Sandtraps, the Headcrab in the last pipe being replaced by a Fast Zombie. The Apache scene is also mirrored at the end of Lost Coast.
- The player can make the Chopper destroy itself by letting it see you when it first arrives in the map, firing rockets at you, and the rocks (which kill the Chopper as it is in the explosion radius.
Beta rendering of the cliffs in Surface Tension.
 Chapter 13: "Forget About Freeman!"
- "Forget about Freeman! We're abandoning the base! If you have any last bomb targets, mark them on the Tactical Map, otherwise, get the hell out of there!"
- ―HECU commander
The HECU, after having taken heavy losses in their battle against the Xen aliens, and continually failing to neutralize Freeman, abandon their mission and begin to evacuate the facility, calling in air strikes and heavy artillery to cover their retreat. Gordon makes his way into an underground storage garage to avoid the bombardments, and navigates his way through underground water channels, fighting his way through scores of aliens and the remaining HECU forces, before finally reaching the Lambda Complex.
- The old level name featured on Half-Life: Day One, given in the "titles.txt" file was: "You're on your own".
- HECU officer, radio operator that gives the orders to Cooper, near the end of the previous chapter Surface Tension says folowing text: "Come in, Cooper! Do you copy? Forget about Freeman! We're abandoning the base! If you have any last bomb targets, mark them on the Tactical Map! Otherwise, get the hell outta there! Repeat: we are pulling out and commencing air strikes! Give us targets or get below!". From sentence in the text comes the name of the eponymous chapter.
- In Half-Life:Opposing Force, this event is mentioned again, however, Adrian Shephard was at the military checkpoint when the HECU officer transmitted the message at the radio, making a focal point of the two games.
- The chapter name is mentioned again in another, more frantic radio transmission. This transmission seems to have been to all troops, and is as follows: "Forget about Freeman! We are cutting our losses and pulling out! Anyone left down there now is on his own. Repeat; if you weren't already, you are now- *transmission is lost*"
 Chapter 14: Lambda Core
The player's first interaction with the newly developed portal technology.
The teleport chamber in the Lambda Complex.
Gordon arrives at the Lambda Complex, but instead of the science team, he finds that the majority of the complex is now overrun by hostile creatures. He is informed that he must flood the reactor chambers in order to access the core, and that a team of scientists is waiting for him at the tip of the reactor. Gordon navigates through the Lambda Core, facing numerous assaults from the Xen forces, now the primary enemy after the evacuation of the HECU.
After much struggle, Gordon finally reaches what is left of the science team, where he discovers that the Lambda Complex is where the teleportation technology that allowed scientists to travel to Xen was developed. The handful of surviving personnel, who have held themselves up in a small stronghold, inform Gordon that the satellite he launched was not able to reverse the effects of the Resonance Cascade because an immensely powerful being on the other side was keeping the portal between the worlds open, and that Gordon must kill it to prevent the Xen aliens from taking over completely. Before being teleported to Xen, arms himself, and is reunited with the Long Jump Module (not seen since the Hazard Course). After an attempted interception by Alien Controllers, the scientists activate the teleporter and Gordon is teleported to Xen.
 Chapter 15: Xen
Gordon finally reaches Xen.
Gordon Freeman arrives in the borderworld, Xen.
On the strange borderworld, Gordon encounters many of the aliens that had been teleported into Black Mesa in their natural habitats, as well as the remains of several HEV-clad researchers that had come before him. Gordon makes his way across the borderworld in search of the creature holding the portal open.
 Chapter 16: Gonarch's Lair
Gordon Freeman faces the Gonarch.
As Freeman makes his way through Xen, he is forced to fight a large alien creature, the Gonarch, in her lair. After killing it, Gordon continues his search.
It is possible that Gonarch's Lair was originally placed after Interloper because Gonarch's Lair map names start from c4a2, while Interloper map names start from c4a1a.
 Chapter 17: Interloper
First view of the Alien Grunt cloning facility.
Gordon's continues his journey across Xen. Along the way, he comes across the Xen army's Alien Grunt cloning facility, where the army is created. At the end, Gordon reaches a portal, which he enters.
The Vortigaunts in one of the factories are not hostile towards players, and will ignore them unless attacked.
 Chapter 18: Nihilanth
One of the areas the Nihilanth sends Gordon.
Nihilanth regaining its strength from a Xen crystal.
- "Win... you cannot win..."
- ―The Nihilanth
Gordon is teleported into a vast cave, in which he finally confronts the powerful and mysterious being holding the portal open, the Nihilanth. In the ensueing battle, Gordon destroys the Nihilanth's shield, allowing him to attack its vulnerable brain. As the creature dies, it floats toward the ceiling, and explodes in a giant green blast that overpowers Gordon's senses.
A scientist can be found in one of the areas that Gordon is teleported to by Nihilanth.
- "It's time to choose!"
- ―The G-Man
When Gordon comes to, he is confronted by the G-Man. Both are transported to various locales around Xen, while the G-Man praises Gordon's actions in the borderworld (which he refers to as "a nasty piece of work"). He explains that his "employers" are now in control of the borderworld for the time being, and have authorized him to offer Freeman a job, agreeing that Gordon has "limitless potential". The final teleportation takes Gordon to the same tramcar that he rode on at the beginning of the game, but apparently flying through space at immense speed. Gordon accepts this offer by stepping though a portal, and, finding himself floating in nothingness, hears the G-Man's voice one last time: "Wisely done, Mr. Freeman, I will see you up ahead..." The story continues from this point in Half-Life 2.
Alternatively, the player may choose not to step into the portal in the final scene. This causes Gordon to be teleported into a giant cave facing rows of Alien Grunts and Manta Rays as the game ends with the G-Man's comment, "Well, it looks like we won't be working together. No regrets, Mr. Freeman." Following this scene is a status report saying, "Subject: Freeman; Status: Observation terminated; Post Mortem: Subject declined offer of employment."
- The chapter name "Endgame" is given in the "titles.txt" file and in Half-Life save and load dialogs.
- The rows of Alien Grunts in the non-canon ("bad") ending are not all spawned NPCs. The rear rows of Alien Grunts are actually rendered as sprites.
- Given Gordon's appearance in Half-Life 2, it is heavily implied that the apparent "choice" offered by the G-Man at the end of the game was not a choice at all, but simply an illusion. This was confirmed by Marc Laidlaw in an email response to a fan.
- ↑ Wavelength: E3 Report
- ↑ Marc Laidlaw Vault on the Steam Users' Forums