Callaham said that John, the Space Marine to be played by Karl Urban (best know as Eomer in the Lord of the Rings trilogy), is stationed along with his unit in a research base on an alien planet (the planet is unnamed in the movie unlike the games Doom and Doom 3 which are set on Mars). In the movie he is reunited with his sister, a scientist on the based named Samantha (to be played by Die Another Day villainess Rosamund Pike).
They were separated after an accident that killed their parents and Callaham says, "They are a little estranged" However, strange things are afoot on the base as alien monsters begin to appear and both brother and sister have to put aside their differences in order to survive. Dwayne "The Rock" Johnson will also appear as Sarge, the head space marine, but Callaham warns, "
He is not going to be smiling a whole bunch. You won't see him raise his left eyebrow."