Adrian Shephard, a U.S. Marine, is deployed as part of the HECU squad to the Black Mesa Research Facility to contain the resonance cascade incident and eliminate any witnesses, including scientists and alien threats.
Shephard's squad engages with alien creatures and hostile forces within the Black Mesa facility, facing unexpected resistance from both aliens and surviving scientists.
During a heavy battle, Adrian Shephard becomes separated from his unit and must navigate the facility alone, encountering new threats and allies.
Shephard battles various alien species including headcrabs, vortigaunts, and the alien military forces attempting to control Black Mesa.
Shephard gains access to advanced experimental weaponry and technology within the Black Mesa facility to assist in his survival and mission objectives.
Shephard encounters and aids surviving Black Mesa scientists, forming temporary alliances to navigate the complex and hostile environment.
Shephard confronts and defeats a displacer beast, an aggressive alien predator within the facility that threatens both him and his allies.
Shephard fights through alien-controlled areas to reach and attempt to neutralize the alien command forces operating within Black Mesa.
After multiple failed containment attempts, the decision is made to evacuate the remaining HECU forces and personnel; Shephard is given orders to escape the facility.
To escape, Shephard activates an experimental teleportation device leading to unexpected and unknown dimensions beyond Black Mesa.
