In the year 2026, a portal to an ancient city on Mars is discovered in the Nevada desert. Twenty years later, the Union Aerospace Corporation (UAC) research facility on Mars is attacked by an unknown assailant. Following a distress call sent by Dr. Carmack, a group of United States Marine Corps, led by Sgt. Asher "Sarge" Mahonin, is sent on a search-and-rescue mission to Mars. The team uses the portal to get to Mars. One of the marines, John "Reaper" Grimm, accompanies his twin sister, Dr. Samantha Grimm, to one of the labs within the devastated sector to retrieve data and he learns that the dig site, where their parents were accidentally killed, was reopened and ancient skeletons of a genetically enhanced humanoid race were discovered.