Spoiler alert: These pages contain unmarked plot spoilers. Read at your own risk.
In Half-Life, the player takes on the role of Gordon Freeman, a theoretical physicist employed in the Anomalous Materials lab at the Black Mesa Research Facility, as he takes part in an experiment that goes horribly wrong and causes a "resonance cascade".
- Chapter 0: Hazard Course
- Chapter 1: Black Mesa Inbound
- Chapter 2: Anomalous Materials
- Chapter 3: Unforeseen Consequences
- Chapter 4: Office Complex
- Chapter 5: "We've Got Hostiles!"
- Chapter 6: Blast Pit
- Chapter 7: Power Up
- Chapter 8: On A Rail
- Chapter 9: Apprehension
- Chapter 10: Residue Processing
- Chapter 11: Questionable Ethics
- Chapter 12: Surface Tension
- Chapter 13: "Forget About Freeman!"
- Chapter 14: Lambda Core
- Chapter 15: Xen
- Chapter 16: Gonarch's Lair
- Chapter 17: Interloper
- Chapter 18: Nihilanth
- Chapter 19: Endgame
In Opposing Force, the player takes on the role of Adrian Shepard, a United States Marine corporal of the Hazardous Environment Combat Unit, who crash lands in Black Mesa and wakes up just as orders start coming in for his outfit to evacuate the facility.
- Chapter 0: Boot Camp
- Chapter 1: Incoming
- Chapter 2: Welcome to Black Mesa
- Chapter 3: "We Are Pulling Out!"
- Chapter 4: Missing in Action
- Chapter 5: Friendly Fire
- Chapter 6: We Are Not Alone
- Chapter 7: Crush Depth
- Chapter 8: Vicarious Reality
- Chapter 9: Pit Worm's Nest
- Chapter 10: Foxtrot Uniform
- Chapter 11: The Package
- Chapter 12: Worlds Collide
- Chapter 13: Conclusion
In Blue Shift, the player takes on the role of Barney Calhoun, a mid-ranking security guard of Black Mesa who enlists the help of one Dr. Rosenberg to escape the facility after all hell breaks loose.
In Decay, the player takes on the roles of two Black Mesa employees assigned to the Anomalous Materials lab: the senior physicist, Gina Cross, and her colleague, Colette Green.
In Half-Life 2, the player returns as theoretical physicist Gordon Freeman, who awakens from indefinite stasis and finds himself in City 17, one of the few remaining cities in a world now under the control of an oppressive alien race known as the Combine.
- Chapter 1: Point Insertion
- Chapter 2: "A Red Letter Day"
- Chapter 3: Route Kanal
- Chapter 4: Water Hazard
- Chapter 5: Black Mesa East
- Chapter 6: "We Don't Go To Ravenholm..."
- Chapter 7: Highway 17
- Chapter 8: Sandtraps
- Chapter 9a: Nova Prospekt
- Chapter 9b: Entanglement
- Chapter 10: Anticitizen One
- Chapter 11: "Follow Freeman!"
- Chapter 12: Our Benefactors
- Chapter 13: Dark Energy
In Episode One, the player continues the role of Gordon Freeman as he moves to escape City 17 before the Citadel's destruction.
In Episode Two, the player continues the role of Gordon Freeman as he fights his way through dense forestry to reach the resistance stronghold, White Forest, with some important intel in tow.
In Portal, the player takes on the role of Chell, a test subject of Aperture Science, who is tasked by the artificial intelligence GLaDOS to take part in a series of tests revolving around the use of the Aperture Science Handheld Portal Device.
In Portal 2, the player returns as the Aperture Science test subject Chell, who has awoken from stasis and is forced by the newly awakened GLaDOS to solve a new variety of tests.
In Portal 2's co-op mode, two players take on the roles of Atlas and P-body, artificial-intelligence robots, who are built and tasked by GLaDOS to carry out a series of tests that require cooperation between the two robots to pass each challenge.