Gears of War takes place on the Earth-like planet Sera, where the discovery of an underground fuel called Imulsion triggered a long global war. Years later, humanity faces a new enemy on Emergence Day, when a subterranean race known as the Locust Horde surfaces and begins a genocidal assault, forcing the ruling Coalition of Ordered Governments to make desperate sacrifices to survive. The story follows Marcus Fenix, a soldier reinstated into the military after being imprisoned for abandoning his post to try to save his father. Freed by his close friend Dominic Santiago, Marcus rejoins Delta Squad and is sent on a dangerous mission to map and strike at the heart of the Locust tunnels, hoping to turn the tide of the war.