Go back one year from the events of S.T.A.L.K.E.R.: Shadow of Chernobyl. In Clear Sky, a group of stalkers has reached the heart of the Zone – Chernobyl Nuclear Power Plant. An immense blowout of anomalous energy changes the Zone. There are no more reliable and relatively safe roads. 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. Changes of the Zone map known to stalkers shake the fragile balance of forces in the Zone. Among the groupings, there flare up hostilities for the new territories, artifact fields and spheres of influence. Everyone is now out for himself. You are a mercenary who appeared at the edge of the opposition between stalker factions, Strelok and the Zone itself. You play the key role in the events that led to creation of the Zone up to the point from which the original S.T.A.L.K.E.R. game begins. Which faction will take the upper hand?