Episode One offers a new single player experience created by Valve, and is designed to be four to six hours in length. Stepping into the hazard suit of Dr. Gordon Freeman, you face the immediate repercussions of your actions in City 17 and the Citadel. Alyx Vance and her robot, Dog, will accompany you in your efforts to aid in the human resistance's desperate battle against the totalitarian alien menace of the Combine.