Once again, if you don't own this game then please do so before you get eaten alive by Gaben.
Half-Life 2: Episode One is the continuation of the very amazing game, Half-Life 2 and is set shortly after the events at the end of Half-Life 2.
The game begins with you smothered in rubble and with low health, a bit near dying point and you hear your female companion's voice, Alyx call out for your name, shortly after her robotic machine simply named DOG finds you and brings you out of the rubble and into the the rather gritty light of the sky, you notice some things are wrong, as you glimpse of the sky once again you also notice and begin to say "What the f**k is happening with the Citadel?" well good question, after your little cat fight with Breen at the end of Half-Life 2, the Citadel has went into meltdown since Breen's teleporter went all fuzzy and simply blew up, thanks to you. And so after getting your head back into the world, your mission is to once again survive the mess you created and get the Hell out of City 17, the aim of the game is to go back inside the Dragon's Nest (the Citadel) and activate the dark fusion powered core that resides deep within the belly of the beast, once you do this you have a lot of time on your hands to get out of the city, you will fight through the Citadel, then in the underground tunnels filled with zombies and with a new special type of zombie, the Zombine, and then you will fight the Combine's last stand forces head on towards the train station, where you are meant to be heading and then after a final confrontation with the Combine, you finally escape and you look back and see City 17 for the last time as the Citadel explodes into peices, the game ends with Alyx's voice whisper "Gordon" and then the events of Half-Life 2: Episode Two begin.
I definitely recommend this game as I do with every Half-Life game, please pick it up if you haven't already, Gaben will forgive your mistakes.