Half-Life 2: Episode One (PC) Walkthrough Undue Alarm

Half-Life 2 Episode One is the first episodic game which takes us to Half-Life 2 world after blowing up dark fusion reactor in the Combine citadel. It was developed and released by Valve in 2006. This add-on continue original Half-Life 2 story and also offers new opportunities and puzzles based on physics (using physics modules developed by Havok).