I rather enjoyed the mix of murder-mystery and the paranormal. Kara is a summoner of demons, demons which have absolutely nothing to do with religion or satanic rituals, which I was quite happy about. These demons do not play by human rules and the summoners respect this fact. Kara is relatable, at least to me, and she is down to earth and quirky. I liked all of the characters, even the demons. There were some twists and turns in the book that kept you guessing as to who was the Symbol Man. Some negative reviews seemed to dislike that you could not guess the murderer--since when is that a BAD thing in a murder-mystery?
The summary of the book kind of leads you to believe that this is a paranormal-romance book, however, it is not. It does contain some sexual context but it is certainly not a romance.
Overall this book kind of reminded me of the J.D. Robb In Death series mixed with paranormal/urban-fantasy rather than the future. Mark of the Demon was an enjoyable, quick read and a series I will surely read more of.