Loosely based on the video game series of the same name by id Software.
A team of space marines known as the Rapid Response Tactical Squad, led by Sarge, is sent to a science facility on Mars after somebody reports a security breach. There, they learn that the alert came after a test subject, a mass murderer purposefully injected with alien DNA, broke free and began killing people. Dr. Grimm, who is related to team member Reaper, informs them all that the chromosome can mutate humans into monsters -- and is highly infectious.
A group of UAC Marines responds to a distress call from a top-secret scientific base on Phobos, a Martian moon, only to discover it's been overrun by demons.
