In the 1900s, an insect-like alien race known as the Chimera arrive in Russia. Using advanced technology, they infect hundreds of innocent civilians and subject them to artificial evolution, creating a diverse army of creatures ranging from simple foot soldiers to spider-like giants. By 1949, all of Europe has fallen to the Chimera. The following year, a vast invasion force tunnels under the English Channel, conquering much of England and leaving only scattered pockets of human resistance. In 1951, the United States, despite taking a position of neutrality in the conflict, sends a task force to assist the UK as part of "Operation Deliverance". Among the soldiers is Army Ranger Sgt. Nathan Hale. However, soon after landing in York, he and his squad are ambushed by enemy troops, who infect them with the Chimera virus. Hale, the only survivor, discovers that he has an innate resistance to full infection. Instead, he gains increased strength and reflexes, the ability to instantly heal light injuries, and gold-colored irises, a common trait of the Chimera.