The game begins with an unconscious, wounded stalker (the player character) being brought to Sidorovich, a black-market trader operating inside the Zone of alienation (or simply "The Zone"). Sid is able to save his life, but the wounded stalker is amnesic, the only clues to his identity are a tattoo on his arm of the acronym "S.T.A.L.K.E.R." and his PDA which contains only one entry in the to-do list: "Kill Strelok." The amnesiac stalker is dubbed "Marked One" by Sid.