The game begins in Iraq, with protagonist Captain Aeran Pierce and his Delta Force Echo Squad (consisting of Lieutenant Logan Somers, Corporal later Sergeant Cody Grayson, and Sergeant later Lieutenant Mitchell Ambrose) on a mission to investigate an underground bunker where W.M.D.s are supposedly stored. The team is assisted by the head of an elite science team; Special Operative Doctor Noa Weis. After battling through Iraqi Republican Guardsmen, Echo Squad reaches the top-levels of the facility where the weapons are supposedly kept, and enter, and soon battle horribly mutated humans and alien creatures (later classified as "Xenos") infesting the top levels of the facility. The team wonders where they came from, but Weis declares the matter classified and dismisses the humans' mutations a