In this chapter, Gordon learns that a satellite has been equipped to reverse the effects of the resonance cascade by the science team, and is ready to be launched into space. However, before the science team could launch the rocket, the Marines arrived and killed them. It is up to Gordon to traverse the rail system and reach the satellite control room to initiate the launch. As Gordon finally emerges from the tunnels at the end of his quest, he finds that night has fallen: it has been a full day since the Resonance Cascade.
On A Rail is the eighth chapter of Half-Life.
The player will have to use a tram to traverse certain sections of the level.
The abandoned railway tunnels are labyrinthine, and difficult to traverse on foot due to the hazard posed by the electrified rail. In the first section of the rail system, Gordon finds himself alone with hoards of aliens.
After Gordon has activated and traversed a tram lift, he finds that the upper level has been occupied by the Marines. Gordon spends the remainder of the chapter engaged in fast firefights in the cramped tunnels, dodging their rockets, and avoiding the traps they've set, occasionally fighting the odd-looking aliens that teleport into the tunnels.