The Postcard Killers by James Patterson and Lisa Marklund
Jacob Kanon is an NYPD detective at the end of his rope. He has become an alcoholic and each day puts his gun in his mouth hoping to end his misery, but won't pull the trigger until his daughter Kimmy's killers are found. Jacob is on the hunt for a pair of ruthless killers moving through Europe killing young couples and sending postcards and clues to newspaper reporters as they go.
With the help of Dessie Larsson, Swedish newspaper reporter, Jacob tracks the killers to Stolkholm in a race against time to stop the killers for good.
This was another entertaining and fast-paced Patterson. Not my favorite, but it kept me engaged.