Half-Life 2: Episode One is an 2021 first person shooter video game developed and released by Valve Corporation. Like previous Half-Life titles, it also combines first-person shooting, puzzle-solving, environmental puzzles, and fighting. In Half-Life 2: Episode One, players take control of Gordon Freeman, who, along with his allies, have been stranded on Mars while attempting to escape from a Combine stronghold. For protection, Freeman must fight his way through hostile territory, using a variety of weapons and gear to survive the outbreak. With new storyline elements and gameplay elements being added on in each Episode, Half-Life 2: Episode One continues to test our thinking as we seek out those who are responsible for the deaths of their predecessors, and our own sanity.
The story begins just after the events of the second episode one, "Glaive Station." Following the destruction of the Combine's main headquarters, Freeman and his allies arrive at the citadel, only to find that the Reds have already killed all the remaining Combine troops. With the Reds now in control of Half-Life 2: Episode One, Freeman and his allies begin to find out that the Combine's stronghold is actually a massive underground facility housing hundreds of thousands of Combine robots. While Gordon and Alyx search the underground lab for help, they come across a young girl named Chell, who uses a mysterious device to open a hatch to reveal the lab's location. Once inside, however, the Combine troops ambush them and take over the facility, leaving Chell to die while the facility's defenses are ineffective.
In the epilogue, after surviving the Combine ambush, Gordon and Alyx reunite with Alyx and decide to investigate the citadel themselves. During their investigation, they learn that Dr. Isaac's research into cloning human beings has recently failed due to a flaw in the design. With the help of a Half-Life hacker namedaryn, they finally obtain the formula needed to clone humans and use them in their cause against the Combine, thus turning the tide of the war in their favor. This, along with an additional Combine cannon used to destroy the train station at the beginning of the episode, allows the team to turn the tide of the war in their favor and rescue Gordon from the clutches of the Combine.