Olduvai Research Station is a remote scientific facility on Mars where something has gone terribly wrong. All experiments have ceased, and communication has failed. The few messages that do get through are less than comforting. It's Level 5 Quarantine, and the only souls allowed in or out are the Rapid Response Tactical Squad (RRTS)--hardened Marines armed to the teeth with enough firepower to neutralize any enemy--or so they think. The researchers at this Red Planet station have unwittingly opened a door, and all hell has broken loose. A legion of nightmarish creatures of unknown origin lurks in every corner and stalks the countless rooms and tunnels of the facility, killing what few people remain. A hellish zoo of demons, Imps, Barons and Hell Knights has taken over Olduvai. And they're not giving it back without a fight. Sealing off the portal to Earth, Sarge, Reaper and their mercenary team must use every weapon at their disposal--and some they find along the way--to carry out their orders: nothing gets out alive. Unfortunately, these things never go as planned.