Doom has been my childhood game and I have played it all day and night.

Immediately following the events in Doom, the player once again takes the role of the anonymous space marine who has proven too tough for the forces of Hell to contain. After being teleported from Phobos, and subsequently fighting on Deimos which is hanging on top of Hell itself, the Marine is back home on Earth, only to find that it too has fallen victim to the hellish invasion.

The player progresses through 30 levels and on the way he learns that the remaining survivors of Earth's population are being held on Earth and the only means of escape is the space port with massive ships that can carry the remnants of Earth's population into space. However the demons know this and have placed a fire force field over the space port, so those ships cannot land or leave. The marine must battle his way through the infested space port and deactivate that fire force field. Once humanity is finally evacuated from the ravaged, infested planet, the Marine is the only human left on Earth. He sits and waits for death, content in the knowledge that he has saved his species, giving them a chance to continue on elsewhere. Only minutes pass before the Marine receives an off-planet transmission - humans in orbit have managed to find out where the armies of Hell are spilling from. If the Marine can reach this gateway, he can thwart the invasion once and for all.

The Marine wearily pulls himself to his feet and moves off to the portal, cutting a swath through the demons in his path before finally arriving at the gateway. He sees no way to close it on this side, and so dives through to find a solution on the other side. In the game's own words, "what do you care if you have to go through Hell to get to it?"

After brutal battles with legions of Hell, the Marine finally reaches the home of the "largest demon (he has) ever seen." Once the player fires enough rockets into the exposed brain of the demon, dodging constant attacks from lesser demons the larger one summons, the demon (known as the 'Icon of Sin') explodes, devastating Hell in its death throes. When the chaos finally ceases, Hell is in ruins, the invasion permanently halted. The Marine wipes his brow and begins the long journey home, looking forward to helping rebuild Earth.