Knots and Crosses By Ian Rankin

 'And in Edinburgh of all places. I mean, you never think of that sort of thing happening in Edinburgh, do you...?' 

'That sort of thing' is the brutal abduction and murder of two young girls. And now a third is missing, presumably gone to the same sad end. Detective Sergeant John Rebus, smoking and drinking too much, his own young daughter spirited away south by his disenchanted wife, is one of many policemen hunting the killer. 

And then the messages begin to arrive: knotted string and matchstick crosses - taunting Rebus with pieces of a puzzle only he can solve.