"X" marks the spot of a vicious killer, his calling card the letter carved on his victims' backs. While the killings are morbid, they also offer detective Tom Thorne plenty of clues. This is turf warfare between North London gangs; organized crime boss Billy Ryan is moving into someone else's patch. Thorne also agrees to help out ex-DCI Carol Chamberlain on an old murder case involving the immolation of a schoolgirl. But soon the two separate investigations begin to fuse into one new, very nasty riddle involving a murderous family that values nothing but its own power. When an "X" is carved on his front door, Thorne knows these crimes of past and present will soon engulf him, too.