From the preview: "After lengthy delays and extensive refactoring, S.T.A.L.K.E.R.: Shadow of Chernobyl hit the ground running and won over all but the most disgruntled fans and critics. It put players in the shoes of Strelok, an amnesiac stalker just trying to get by in the unforgiving Zone. The Zone was rendered uninhabitable first by the catastrophe at the Chernobyl Nuclear Power Plant. Still, stalkers were able to enter the Zone in search of relics until they brought about another catastrophe-a release of inexplicable energy that rendered some areas impassible, trapped stalkers in the Zone, and even created other, unknown areas. It's after this second event that S.T.A.L.K.E.R.: Clear Sky begins, one year prior to the story of Shadow of Chernobyl. Yep, it's a prequel, but it's not afraid to change the rules of the Zone in order to keep players guessing and give them a new experience in the Zone."