Conquest - The Godsverse Chronicles, #9

The Lords of Hell collude to ruin Katrina and end her reign as Devil.  Katrina has been the Devil for over 150 years, and the demons of Hell hate her. Not only is she a woman, and a human, but she's trying to modernize Hell, bringing technology to Dis, and treating monsters like employees instead of slaves. Blasphemy to the natural order. A conspiracy congeals to take down Katrina by summoning the Four Horsemen and initiating the cataclysmic destruction that is Ragnarök. If the demon dukes succeed, the Universe is doomed. Only Katrina, Julia, Akta, and Kimberly have any chance of stopping the world from descending into chaos.  Join these four heroes as they smash, kick, punch, and generally battle to save Earth in this epic team-up book.
If you love action, adventure, magic, and demons, then Conquest is for you.