Half-Life 2: Episode One Chapter 5: Exit 17

In that final chapter set in the Technical Trainstation, Gordon helps evacuate Citizens and Rebels and fights a Strider blocking the train tracks. The Citadel blows at the end of the chapter, and its shockwave overtakes Alyx and Gordon's train.

Upon reuniting with Barney at the train station, Alyx and Gordon work to move the Citizens to the trains while facing increasing Combine opposition. They then decide to stay behind to lure the Combine away from Barney and the citizens as they board the train and make their escape.

After battling Combine soldiers and a Strider, the duo reprogram another train and board the caboose. As the train carries Alyx and Gordon away, the Citadel is visible in the background with the reactor core once again about to explode, and the Combine's message is sent. Several Advisor Pods are ejected from the Citadel as it detonates. On two occasions, as pods pass overhead, Gordon and Alyx are hit with psychic blasts. The force of the shockwave from the exploding Citadel causes metal chunks and wreckage to fly toward the train Alyx and Gordon are on as it sends its final transmission, and the screen fades to an ominous white as the Citadel explodes, destroying City 17, and causing a shockwave that overtakes the train. The last thing that the player hears is the twisting of metal and Alyx whispering Gordon's name.