Set on the planet Sera some months after the previous game, the war between humanity and the underground Locust Horde reignites when Locust forces begin sinking entire cities. With the last major human stronghold under threat, the Coalition of Ordered Governments launches a large offensive to take the fight into the depths of the planet. Sergeant Marcus Fenix leads Delta Squad underground to strike at the Locust directly, while his comrade Dom Santiago continues a personal search for his missing wife.