Doom 3 is set on Mars in 2145, where a powerful corporation runs a research facility experimenting in areas such as teleportation, biological research, and advanced weapons, often outside legal and ethical limits. The player takes the role of a newly arrived space marine assigned to routine duties at the base. When a teleportation experiment loses containment, a gateway to Hell is torn open and the facility is overrun, transforming much of the personnel into hostile creatures. Cut off and outnumbered, the marine must fight through the base to survive, uncover what the experiments unleashed, and stop the invasion from spreading beyond Mars.