Immediately following the events in Doom, the player once again assumes the role of the unnamed space marine. After defeating the demon invasion of the Mars moon bases and returning from Hell, Doomguy finds that Earth has also been invaded by the demons, who have killed billions of people. The humans who survived the attack have developed a plan to build massive spaceships which will carry the remaining survivors into space. Once the ships are ready, the survivors prepare to evacuate Earth. Unfortunately, Earth's only ground spaceport gets taken over by the demons, who place a flame barrier over it, preventing any ships from leaving.