You were transported to Mars along with your comrades to clean out the Mars base, it is full of demons, you're lucky that you are with your comrades there, else it would be a tough mission, after you are done with all that, you will have to destroy the Mastermind behind those demons, good luck.
Id Software, and creators of doom builder and XWE
New from scratch.
Doom Builder and XWE
If the Mastermind gets stucked in the wall at the final boss fight, you will have to restart the level.