Poke646 (2001)

Thirteen months after the Black Mesa incident, the research facility has been shut down. The nation never got to know anything about the experiments there, and the governement created a organisation specificly to handle "Alien Related Topics". The name of that organisation is Poke646. Unfortunately aliens are invading Nation City with portals, and Damien Reeves is the only Poke646 member who didn´t evacuate, due to an accident. Guided by a man named Dr. Sebastian Fuller through Poke646's radio transmitter, he must turn on 4 generators in the city to stop the portals from coming.