Dark, so so so dark. I think the relationship between the love interests has been developed very well.  What the story really lacks is the background to build the relationship between the two duelling San Francisco serial killers.  As much as the leading man rejects the other San Fran serial killer their story is as central to the plot as the smutty romance, and that aspect of this story is seriously underdeveloped. I am desperately hoping the second book builds both that story and the romance.