When the decomposing body of a young woman is found, the wounds on her wrists suggest an open-and-shut case of suicide. But Jack Caffery is not so sure. Other apparent suicides are cropping up, and they all have a connection to Elf's Grotto, a nearly bottomless network of flooded quarries just outside the city. Caffery begins to suspect a shadowy and sinister predator, someone - or something - that can disappear into darkness and slip into houses unseen. Working alongside Caffery is rough-and-tough police diver Flea Marley, but while pursuing her investigation, she stumbles upon something far too close to home that no one - not even Caffery - can help her face.