PLOT

SPOILERS AHEAD!
YOU HAVE BEEN WARNED!

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Overview

The game is set during May 200- in a remote area of New Mexico, USA at the Black Mesa Research Facility a fictional complex that bears many similarities to both the Los Alamos National Laboratory and Area 51.

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Part 1

"So, wake up, Mr. Freeman. Wake up and smell the ashes." - The G-Man

Early in the morning, Dr. Gordon Freeman, a recent MIT graduate in theoretical physics, and also a recent employee at Black Mesa, arrives late at the Anomalous Materials lab to participate in an experiment that involves analyzing an alien crystal. After the test goes "unexpectedly" wrong, a catastrophic event called a Resonance Cascade occurs and causes massive dimensional rifts, opening a portal between Earth and Xen. Saved by his HEV Suit from the devastating chaos at ground zero, Gordon leaves the test chamber and is tasked with reaching the surface by Eli Vance and getting help. Soon, he finds out that the facility is infested with dangerous and hostile alien creatures. Arming himself, Gordon starts his journey to the surface..

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Part 2

As the situation escalates, Gordon finds himself caught between two opposing factions: the hostile aliens, and the Hazardous Environment Combat Unit, a military force dispatched to cover up the incident — including eliminating Freeman and the rest of the Black Mesa Science Team. Throughout the game, a mysterious figure known as the G-Man regularly appears, apparently monitoring Freeman's progress with uncanny serenity. Gordon successfully launches a rocket meant to close the dimensional rifts. This stops the random teleportation of aliens, but also alerts them that their connection to Earth is limited, causing a full organized invasion by Xen.

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Part 3

As the situation escalates, Gordon finds himself caught between two opposing factions: the hostile aliens, and the Hazardous Environment Combat Unit, a military force dispatched to cover up the incident — including eliminating Freeman and the rest of the Black Mesa Science Team. Throughout the game, a mysterious figure known as the G-Man regularly appears, apparently monitoring Freeman's progress with uncanny serenity. Gordon successfully launches a rocket meant to close the dimensional rifts. This stops the random teleportation of aliens, but also alerts them that their connection to Earth is limited, causing a full organized invasion by Xen.

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Part 4

Gordon fights his way through the facility and at one point even deals with the Black Ops assassins sent to eliminate all the scientists, aliens, and HECU marines. Gordon is ambushed by HECU marines just before reaching the surface and is left to die in a trash compactor. Luckily, Gordon escapes, and winds up fighting his way through the Biological Waste Processing Plant of Black Mesa and eventually comes upon a secret sector of the facility where he discovers that scientists had been "collecting" specimens from Xen since long before the incident occurred. Cooperating with surviving scientists and security officers, Gordon ultimately works his way to the mysterious Lambda Complex, where a team of scientists teleports him to the alien border world of Xen, where he must destroy the Nihilanth, the creature keeping Xen's side of the dimensional rift open.

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Part 5

After reaching the alien dimension and fighting hordes of different alien monsters, including the mother of all headcrabs, The Gonarch, Gordon manages to reach the portal that takes him to Nihilanth's chamber. After a challenging battle, the scientist gains the upper hand and finally destroys the creature. As the creature explodes, Gordon suddenly gets teleported.

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Part 6

After reaching the alien dimension and fighting hordes of different alien monsters, including the mother of all headcrabs, The Gonarch, Gordon manages to reach the portal that takes him to Nihilanth's chamber. After a challenging battle, the scientist gains the upper hand and finally destroys the creature. As the creature explodes, Gordon suddenly gets teleported.