The Bloodgate Guardian by Joely Sue Burkhart
Dr. Jaid Merritt's father has mysteriously disappeared...into a portal after performing an ancient Mayan ritual...and she saw it all on her webcam. Jaid heads to her father's dig site (overcoming a childhood fear of digs), to try and find a way to bring him back.
Instead, she stumbles upon an ancient priest, and by ancient I mean thousands of years old, but still amazingly handsome, named Ruin. Ruin is the guardian of the gate her father inadvertently crossed through, which also allowed a few demons from hell into the world.
Jaid and Ruin rush to find a way to close the gate and save their loved ones from eternal torment at the hand of the demons, and to save the world from being devoured by the demons that escaped.
This is an Indiana Jones meets romance style of book, and the author really pulled it off very well. A great read (and not gory), full of action, adventure, mystery, and romance.