Half-Life: Opposing Force storyline
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This article describes the Half-Life: Opposing Force storyline, chapter by chapter.
The story of Opposing Force cleverly interweaves with the events of Half-Life, so that the player catches a glimpse of Gordon Freeman, the main character from the original game. Shephard sees an officer making a pivotal radio broadcast that Freeman overhears in the first game, and visits some recognizable locations.
In the original Half-Life, a Resonance Cascade opens an extra-dimensional rift, which cause Xen aliens to teleport into the Black Mesa Research Facility. The surviving scientists and security guards at the facility struggle to escape. Responding swiftly, the United States military initiates a massive "clean-up" operation to eradicate the alien presence at Black Mesa as well as "silence" any witnesses.
 Boot Camp (optional)
The training chapter of Opposing Force. Adrian Shephard is bumped to the top of the Advanced Training list. Shephard and his comrades are trained by Dwight T. Barnes, Marine Drill Instructor, in Santego Military Base, Arizona. He works his way through the training exercises overlooked by Drill Instructor Sharp until he is ready for the field.
 Chapter 1: Incoming
As the game begins, Shephard is part of the clean-up operation. After his transport aircraft is taken down by an Alien Craft and he is cut off from the rest of his unit, the "clean-up" mission is abandoned and Shephard joins forces with the scattered survivors seeking escape.
Before the first chapter of Half-Life: Opposing Force, a short introduction is shown. As Adrian Shephard and his fellow HECU comrades are approaching the LZ (Landing Zone 117) at the Black Mesa Research Facility, his plane (codenamed Goose 7) is shot down by Alien Crafts, along with several other Osprey Heliplanes (the first one is codenamed Goose 3). The rest of the opening sequence consists of Shephard continually losing and regaining consciousness, seeing conflict between the Xen aliens and the Marines who survived the crash.
- The canyon wall from the first part of the Half-Life chapter Surface Tension, which Gordon used to get to the Lambda Complex, can be seen.
- The chapter name "Incoming" is given in the "titles.txt" file.
 Chapter 2: Welcome To Black Mesa
After the crash of his Osprey Heliplane, Adrian Shephard regains consciousness completely in an infirmary, not too far off from the crash site. He leaves the infirmary, learning that the other Marines who had survived the crash had been killed by the aliens. He makes his way towards the extraction point, where he is told via radio that the military forces are pulling out of the facility.
 Chapter 3: "We Are Pulling Out"
As the battle begins to favor the Xen aliens, Shephard realizes the military forces have been ordered to pull out.
Details Adrian Shephard's attempt to reach the HECU's extraction point to escape Black Mesa. He has first eye contact with the mysterious Race X that seems to be collecting humans for study in their world. Shephard reaches the extraction point, but is deliberately left behind due to the G-Man's actions.
The player facing two zombie security guards in a crumbling hallway.
- This chapter takes place at the same time as the Half-Life chapter Surface Tension.
- The radio operator heard at the end of Surface Tension appears just before the end of the level, meaning that Gordon reaches the Tactical Map by the time Shephard arrives at the operator's room making the announcement.
 Chapter 4: Missing in Action
Details Adrian Shephard's continued journey through Black Mesa in search of both his comrades and an alternative escape route after being abandoned at the extraction point. After traveling through a zombie-infested blast furnace, Shephard meets several other Marines from his company who have also been left behind. He joins forces with them as they try to escape from the facility. At this point, Race X have begun their own invasion amidst the chaos, slaughtering the stragglers.
 Chapter 5: Friendly Fire
Details Adrian Shephard and other HECU soldier's attempt to find and use an old transit system to escape to the Lambda Core, after battling through an office complex filled with aliens. It is also the chapter in which the Black Ops are first introduced. Shephard comes across them in a hangar where they are loading a nuclear warhead into the back of a truck. This is where the player learns that the Black Ops soldiers have been sent to kill the remaining HECU Marines and cover up the Black Mesa incident. Shephard meets up with several other surviving marines and fights the Black Ops, eventually reaching an underground railway system that leads to the Lambda complex.
- This chapter takes place at the same time as the Half-Life chapter Lambda Core.
- In an office, two dead scientists can be seen lying in front of their desks. Their names are S. Reardon and S. Jones, a nod to Gearbox employees Sean Reardon and Steven Jones.
- In another office is a picture of Gordon Freeman labeled "Employee of the Month".
- At the very start of the chapter, noclipping out of the map will reveal an empty room with the phrase "What are you doing in my entity room?" sprayed on the wall.
 Chapter 6: We Are Not Alone
It serves as a short interlude in the game with reminders of events from the original Half-Life. Arrived at the Lambda complex, Adrian Shephard sees Gordon Freeman teleported to Xen. Shephard is also forced to travel through Xen to find a way out of the Lambda complex.
- This chapter takes place at the same time as the Half-Life chapters Lambda Core and Xen.
- A Chumtoad is hidden in a vent towards the beginning.
- If you run quick enough, you can follow Freeman through the portal, but you will end up falling to your death in Xen and get the message that you were eliminated to prevent creating a paradox. Also, when entering to Xen, this title will appear "C4A1TITLE". This is referring to Xen's map name, c4a1.
 Chapter 7: Crush Depth
In it, Adrian Shephard finds himself in underwater laboratories where several Ichthyosaurs are being held. After making his way through the labs and freeing a scientist who provides him with information on the area, Shephard is again forced to teleport to Xen and back again to reach a new part of Black Mesa.
- In fluid physics, the term "crush depth" is the depth at which the pressure will be strong enough to crush a mentioned object. Therefore the name is a pun to the design of the level itself, which contains a considerable amount of water.
 Chapter 8: Vicarious Reality
Adrian Shephard is traveling between various biosphere chambers and laboratories featuring massive terrariums used to house Xen fauna being studied by the scientists deep within the Sector E. Eventually he reaches an older industrial area, and picks up a radio transmission from a group of Marines fighting some kind of massive creature.
 Chapter 9: Pit Worm's Nest
Details Adrian Shephard's battle with the monstrous Pit Worm blocking his progress in Waste Processing Area 3. Working his way through the surrounding area (littered with the corpses of the Marines who sent the distress signal in the previous chapter), Shephard manages to dump toxic waste on the Pit Worm, killing it and allowing him to access the next area.
- This chapter mirrors the chapter Blast Pit from the original Half-Life, though it is much smaller.
- The puzzle to kill the Pit Worm involves both a "valve" and a "gearbox" to be used, which are obvious references to the game's developers as an Easter egg.
- Another Easter egg are the garbage compactors, especially the flooded one, which are directly designed after the Death Star's garbage compactor seen in the film Star Wars Episode IV: A New Hope.
- In the first map, a flooded Xen area where one can be brought by the Displacer features two dead scientists. In the second map, another scientist can be found clinging to the edge of an island with another Displacer (that brought him there) still on the island.
- This chapter takes place at the same time as the Half-Life chapter "Nihilanth".
 Chapter 10: Foxtrot Uniform
Details the fierce battle raging between the Race X creatures, the Black Ops contingent, including several snipers, and the remnants of the HECU in the last hours of the Black Mesa Incident. Adrian Shephard makes his way through the underground canals and sewers of Black Mesa, fighting through a Voltigore nest, and arrives at the hydroelectric dam featured in the first game. Here, a Gargantua has been trapped on top of the dam and several Marines are attempting to kill it. Shephard uses explosives to destroy the creature and leaves the area through the dam's exposed water pipes.
The chapter name Foxtrot Uniform is derived from the NATO phonetic alphabet, referring to letters "F" and "U". It is a military euphemism for "fucked up," sometimes preceded by "Alpha" (for "all", represented by "A").
 Chapter 11: "The Package"
This chapter details Adrian Shephard's discovery of the mysterious Black Ops' plan for Black Mesa. He finds them in an underground parking garage, activating the thermonuclear warhead from the fourth chapter, apparently with the intent of destroying the facility. Shephard kills them and deactivates the nuclear bomb, but later sees the G-Man reactivating it. Adding to the Black Ops, Shephard must face heavy artillery, a black AH-64 Apache and Shock Troopers.
 Chapter 12: Worlds Collide
After making his way through warehouses filled with Race X creatures and Black Ops fighting, Adrian Shephard arrives at an old industrial area of Black Mesa where an enormous Gene Worm is attempting to come through a portal from the Race X homeworld. Shephard uses mounted laser weapons to blind and kill it; in its death throes, an enormous teleportation portal spreads outwards and envelops him.
Shephard regains consciousness inside an Osprey Heliplane, confronted by the mysterious G-Man. As the G-Man talks to Shephard a white flash occurs in the distance, indicating that Black Mesa has been destroyed by the nuclear warhead. The G-Man then informs Shephard that he will be detained "in a place where you can do no possible harm, and where no harm can come to you." He explains this is done since Shephard reminds him of himself, but is still a dangerous witness. The G-Man walks into a portal, Shephard is detained and the end credits roll.
 See also
|Half-Life story arc||Half-Life storyline · Half-Life: Opposing Force storyline · Half-Life: Blue Shift storyline · Half-Life: Decay storyline|
|Half-Life 2 / Portal story arc||Half-Life 2 storyline (original storyline) · Half-Life 2: Episode One storyline · Half-Life 2: Episode Two storyline · Portal storyline · Portal 2 storyline|
|Overall||Half-Life and Portal universe · Timeline of the Half-Life and Portal universe · Canon · Recurring themes · Retcons|