Dream Chaser by Sherrilyn Kenyon

"Xypher has one month on Earth to redeem himself through one good deed or be condemned to eternal torture in Tarturus. But redemption means little to a demigod who only wants vengeance on the one who caused his downfall.Until one day in a cemetery....

Simone Dubois is a medical examiner with a real knack for the job. Those who are wrongfully killed appear to her and help her find the evidence the police need to convict their killers. But when a man appears and tells her that she's more than just a psychic, she's convinced he's insane.Now the fate of the world hangs in her hands....

It was bad enough when just the dead relied on her. Now's there's the seductive Dream-Hunter Xypher who needs Simone's help in opening a portal to the Atlantean hell realm to fight insatiable demons. The future of mankind is at stake - and so is her life. The only question now is: Who is the bigger threat: the demons out to kill her, or the man who has left her forever changed?"

Mass market, a nice copy