Richard Montanari is my new favorite mystery author.  Merciless is his 6th novel.  His books are about two homicide detective partners from Philadelphia:  Kevin Byrne and Jessica Balzano.  I like the bond that is between both of these characters.  Very supportive and caring.  Both are descendants of cop families.  Byrne is divorced with a deaf-mute teenage daughter that he adores.  Jessica is part-time pro boxer who is married to a pretty-boy vice cop, who once strayed from his wedding vows, and is trying to save their marriage.  They have a precocious 5-year old daughter.   Montanari's books are always quick-paced and I usually read them at one or two sittings.   Merciless is set in Philadelphia; which can be rough city with a high crime rate.  At times there is a lot of irony in it being known as the City of Brotherly Love.  Merciless is about a serial killer with a Hans Christian Andersen fetish.  If you like mysteries with good character development and a lot of suspense, you enjoy this book.