BLACK MESA

The Black Mesa Incident, also referred to as the Lambda Incident, was a catastrophic event resulting from an experiment carried out by the Anomalous Materials Department at the Black Mesa Research Facility. The experiment triggered a rare quantum event known as a Resonance Cascade, which ruptured the space time continuum and allowed extradimensional beings from a realm known as the Borderworld to teleport into the facility. Black Mesa personnel who had survived the initial incident attempted a resonance reversal using an orbiting satellite to seal the tear. The attempt failed and it was deduced that a powerful being was deliberately holding the rift open. The survivors quickly realized the presence of the aliens was not an accident, and were in fact the vanguard of an invasion. The United States government dispatched a military expeditionary force to the facility to contain the invasion and silence witnesses, however, they suffered heavy casualties and were compelled to quickly withdraw. The ensuing desperate conflict between the survivors and increasing numbers of alien creatures led to the government authorizing the facility's destruction with a nuclear device, which destroyed the facility and eradicated the invasion. Prior to the facility's destruction, Black Mesa scientist Gordon Freeman had been teleported to the Borderworld by the Lambda Team, where he successfully killed the creature coordinating the invasion and holding the rift open. Freeman's whereabouts would remain unknown for decades, as he disappeared immediately after these events. Though Freeman's actions halted the invasion, the portal storms that occurred as a consequence of the incident continued to intensify, ultimately attracting the attention of a powerful interdimensional empire known as the Combine to launch an invasion and subsequent occupation of Earth.
HALF LIFE 2

CHAPTER 1: "POINT INSERTION"

Nearly twenty years after the Black Mesa Incident[1], the G-Man wakes Gordon Freeman from stasis and inserts him (seemingly without any goals) into a train arriving in City 17, a city located somewhere in Eastern Europe under the control of the Combine Empire. After leaving the train, Gordon and the other passengers are welcomed by a broadcast by Dr. Wallace Breen, former administrator of Black Mesa, and now the administrator of Earth. Continuing on his way, Gordon meets armed Civil Protection officers policing the train station and its surroundings. One of them separates him from the rest of the arriving citizens and directs him into a small interrogation room before revealing himself to be former Black Mesa security guard Barney Calhoun, who is operating undercover for the Resistance. Barney contacts Dr. Isaac Kleiner, Gordon's mentor from his MIT days and former Black Mesa employee. After a bit of discussion, they decide to send Gordon over to Kleiner's Lab. Along the way, Gordon finds himself in the middle of a Civil Protection raid on a tenement house; after being captured, Gordon is rescued by a young woman named Alyx Vance.
CHAPTER 2: "A RED LETTER DAY"

Alyx, the daughter of Eli Vance, a former Black Mesa employee now leading the Resistance against the Combine, takes Gordon to Dr. Kleiner's lab. There he is given an H.E.V. Suit and instructed to be teleported to Black Mesa East with Alyx, where he will be able to work alongside other scientists. After teleporting Alyx, Gordon is next, but an interruption from Kleiner's pet Headcrab, Lamarr, causes a malfunction in the teleporter, sending Gordon to Dr. Breen's office, who recognizes him as a threat and puts Combine forces on full alert. Following the failed teleport sequence, Gordon's only option is to go on foot through the old Canals, with Civil Protection officers in hot pursuit. Before starting his journey, Gordon is given a Crowbar by Barney.
CHAPTER 3: "ROUTE KANAL"

With the Crowbar, Gordon is able to disarm two Civil Protection officers who had cornered a couple of Citizens, obtaining in this way his first firearm, the USP Match. Being armed allows Gordon to defeat all Civil Protection Units dispatched to the area before reaching Station 12, one of the many stations set up by the Underground Railroad, a network helping refugees escape City 17. Most of these Stations and outposts are already under attack by the time Gordon arrives; generally filled with Manhacks or being bombarded with Headcrab Shells. Along the way, Gordon obtains his second firearm, the MP7. Eventually, Gordon reaches Station 6 (now under attack by Headcrabs); where he receives the Airboat, a makeshift vessel with an aircraft-type propeller, to help him traverse the toxic system of canals and get to Black Mesa East quick and safely.
CHAPTER 4: "WATER HAZARD"

Aboard the Airboat, Gordon fights off numerous Civil Protection units and a Hunter-Chopper in the river, canals and industrial areas around and outside City 17. Along the way, the boat is upgraded with a pulse gun by a Vortigaunt. After shooting down the Hunter-Chopper in a fight, Gordon Freeman finally reaches his destination, an abandoned hydroelectric power plant on the other side of the dam where Black Mesa East is located.
CHAPTER 5: "BLACK MESA EAST"

Arriving to the Black Mesa East late in the evening Gordon meets Dr. Judith Mossman for the first time, and is reunited with Resistance Leader and former Black Mesa Scientist Eli Vance and Alyx. Gordon is also introduced to the Zero Point Energy Field Manipulator, also known as the 'Gravity Gun', a physics manipulator that quickly becomes indispensable, and after that, Gordon meets Dog, Alyx's robotic "pet." Like A Red Letter Day, this chapter is full of insight and dialogue about the current state of the world, the people in it, and the aftermath of the Black Mesa Incident. While Gordon is playing with Dog in the scrapyard, Alyx spots Combine Scanners sweeping the area, shortly before an all out aerial raid on Black Mesa East. While attempting to rejoin the others, Gordon and Dog are separated from Alyx by a collapsed ceiling, and Gordon is forced to escape down a tunnel to Ravenholm, a place that Alyx didn't want to talk about earlier, showing obvious discomfort at the thought.
CHAPTER 6: "WE DONT GO TO RAVENHOLM..."

Gordon journeys through the tunnel to the ghost town of Ravenholm. Originally a hidden village that lived free from the rule of the Combine, it was discovered by the Combine and attacked by hundreds of Headcrab Shells, thus transforming almost the entire population into deadly Zombies. This chapter also introduces two new headcrab variants - the Poison Headcrab and the Fast Headcrab - and their Zombie counterparts. Freeman kills Zombies and avoids bizarre deathtraps, meeting the man who set them, Father Grigori, who gives Gordon a shotgun. Freeman and Grigori make their way to an old mine which has a path that leads back to City 17, but Grigori stays behind to fight Zombies, and he continues to do so until the crypt behind him bursts open, leaving more zombies to come out from it. He continues to shoot the Zombies for a while until he runs through a blazing fire into the crypt. Gordon navigates the mines ahead, then walks down a railroad avoiding Combine snipers to reach Shorepoint Base.
CHAPTER 7: "HIGHWAY 17"

Freeman is informed that Eli Vance has been taken to Nova Prospekt and sets out on a journey along Highway 17 located in The Coast to rescue him. Gordon encounters Combine Soldiers for the first time as well as a new type of Xen alien, the Antlions that made enormous colonies in the beach areas. Colonel Odessa Cubbage is also met in this level, giving Gordon the RPG. As Gordon navigates through the Highway 17, he sees abandoned outposts taken over by Combine before arriving to the Bridge Point. Gordon deactivates Force Fields in order to progress across a train bridge.
CHAPTER 8: "SANDTRAPS"

Continuing on to Nova Prospekt, Gordon exits a Zombie-infested tunnel, fends off a C