S.T.A.L.K.E.R.: Clear Sky is a survival FPS game for PC based on a 'what-if' scenario of the second Chernobyl Nuclear Power Plant accident. The game is created as a warning to mankind against mindless play with technologies. S.T.A.L.K.E.R.: Clear Sky is the official prequel to the renowned S.T.A.L.K.E.R. game by the Ukraine-based GSC Game World studio. The game is set in 2011 and brings forth the events to have preceded the third campaign of Strelok to the Zone center. S.T.A.L.K.E.R.: Clear Sky introduces an alternative look onto the events of the original game and offers the player to try himself out as a mercenary s.t.a.l.k.e.r. in search of his own path in the world of S.T.A.L.K.E.R.

A group of stalkers has for the first time reached the very heart of the Zone - Chernobyl Nuclear Power Plant, and brings about a cataclysm on the brink of a catastrophe. An immense blowout of anomalous energy changes the Zone. There are no more reliable and relatively safe roads. The entire levels vanish in the outbursts of anomalies. Stalkers and even expeditions die or end up sealed on the lost territories. New areas, which remained unknown since the time of the Zone emergence, appear on the Zone map. The Zone continues to shake with blowouts. The Zone is unstable. The anomalous activity is at its maximum.