Demon Hunter Series by Electa Graham

Jael swears like a sailor, drinks like a fish and gambles like a card shark, but the thing she does best is kill demons. Her goal in life is to remove every last abomination from the face of the Earth. She doesn’t like it when her rich Aunt Bevie insists she take a partner, and she hates it when he turns out to be a young newbie who only wants to hunt for the thrill... moreJael swears like a sailor, drinks like a fish and gambles like a card shark, but the thing she does best is kill demons. Her goal in life is to remove every last abomination from the face of the Earth. She doesn’t like it when her rich Aunt Bevie insists she take a partner, and she hates it when he turns out to be a young newbie who only wants to hunt for the thrill. It isn’t until Cain, the son of Lucifer comes to her in her dreams and tells her she’s the Key to Heaven’s Gate that she realizes she needs all the help she can get. Cain doesn’t just want her to help his father get back into Heaven he wants her to rule Hell with him. Is a chance to rule over all demon kind too good to pass up? less

Most of the time Cole and Jael hunt demons, but Ambrose Barlow is their latest client and he wants them to find part of an ancient tome. This might be the find of a lifetime and allow them to kill the biggest demon of them all. Barlow believes the pages will tell him how to kill Lucifer himself. If there is one thing Jael knows, when something seems to good to be true it usually is.