Hell to Pay is an unofficial commercial add-on for DOOM II, which replaces all 32 original levels and features new music, textures and graphics.
A new plot changes the demons from Hell into an alien race from the planet Hell that attack and conquer the Earth, forcing its inhabitants into slave camps controlled by "trustees", inherently evil humans who are taken away and return as mutants to guard other humans.
The player plays a prisoner imprisoned after a plan to incite a revolt was discovered by the aliens. However your ambition to resist the aliens remains...
Hell to Pay includes new graphics for several player weapons and bad guys to turn them into aliens or alien machines.
It is considered by many to be a "sister" product to Perdition's Gate, a Doom II: Hell on Earth level set released by WizardWorks and Wraith Corporation at the same time.