The first part of the book is much, much stronger than the later part.
The first part begins in the middle ages where Hugh is a young squire newly knighted. Lilith is already a century old demon who is sent to the castle where Hugh lives to send corrupt souls to Lucifer.
Lilith is a Demon who serves but even though she is sarcastic, manipulative and lies alot, you can't really dislike her. Hugh is good, smart and so pure in spirit it practically shines out of him. And even though Lilith should be able to corrupt him she can't. Through a series of events, Hugh is killed and is made a Guardian -- an angel who lives on earth and protects mortals.
The next few chapters details almost 1000 years of the two of them crossing paths, taunting each other, alternately suppressing their feelings or flirting lightly with each other.
This part was really good. I liked the establishment of both their characters, personalities and relationships.
But then we get to the present time and there is a turning point in their relationship that precipitates a life altering event for both characters.
Now they are both on earth as humans. Lilith is an FBI agent and Hugh is a college professor. The remainder of the story becomes a somewhat plot heavy, almost muddled story of Lucifer manipulating Lilith to steal Hugh's soul. Along the way they deal with nosferatu, vampires and a faction of demons who are trying to steal Lucifer's throne.
I thought the second half of the story, especially the overtly byzantine plotline with all the hidden agendas and betrayals bogged the story considerably. I actually struggled to stay interested. The only part that kept me involved was the intense relationship and continued connection between Hugh and Lilith. I have to give the author a lot of credit she did a great job of creating a deep emotional romance between two characters who probably should not be together. And she made them both very likable even in their extreme natures.