S.T.A.L.K.E.R.: Clear Sky Gog.com Key GLOBAL

S.T.A.L.K.E.R. Clear Sky is a prequel to an action shooter RPG S.T.A.L.K.E.R. Shadow of Chernobyl. The action takes place one year before the events of the first game, and while going through campaign, you will find out many things that were left untouched by the events in the 1st game.
What challenges are lying ahead? Why do anomalies continue throughout the zone, and what can you do about it? These and many other questions will be answered in S.T.A.L.K.E.R. Clear Sky!