Still an excellent read, I just wish I'd been better prepared for the level of violence/gore/horror.
Delia sees ghosts. But one in partcular, her "Shadow" follows her all the time, across the country. When she returns to San Francisco to help celebrate her best friend's wedding, Shadow gets demanding.
At the same time, the local police are dealing with a serial killer (ok, this should have been my first warning - I normally avoid books about serial killers). Since the prospective groom is helping with the case, the girls can't avoid being dragged into it. Once the police are convinced that Delia's "talent" for seeing ghosts is real, her help is not only requested, but necessary. Her "Shadow" is the only one who can make the connection between this batch of killings and one that took place a few decades earlier.
I think the author took a chance mixing horror into historical and urban fantasy. It just depends on the reader on whether or not that chance paid off. For me it didn't, but I know a ton of people who will thoroughly enjoy this book.