
If you're on the site and haven't actually seen this movie then I think you may have taken a wrong turn... but if you're here and just curious about Doom, then here's a little plot summary for you. :)
The Doom movie opens with a brief explanation of our setting - the Olduvai research facility, a site based on Mars where the only way in or out is through a teleportation gateway in the Nevada desert. The details are sketchy - no one really knows how or why a gateway to Earth from Mars even exists, but there are people on Mars trying to find that out... and a whole lot more.
The next thing we know, a monster is rampaging through the Olduvai facility, killing off a team of scientists from the shadows one by one. After a gruesome accident with a door, Dr. Carmack, head of the research team, manages to get a message back to Earth - there has been a security breach, and a quarantine has to be imposed on the facility. Shortly after, whatever was hunting him breaks through the metal door, and the transmission ends.
With the stage seemingly set, a team of mercenary soldiers are pulled from leave and told they are to go to Olduvai and clear the facility of any possible threats that may be present. Led by the Sarge (Dwayne 'The Rock' Johnson), and joined late by our reluctant hero John 'Reaper' Grimm (Karl Urban) after a recommendation that he take his leave as planned, the team of soldiers head to Mars to take the facility back - and not let whatever it was that killed the scientists get to Earth.