A crimewave sweeps through the city and no-one is safe. An arson at the docks. A carjacking gone wrong. A murder in a country park. What connects all these crimes without causes, which leave no clues? Detective Inspector Helen Grace faces the rising tide of cases which threatens to drown the city. But each crime is just a piece of a puzzle which is falling into place. And when it becomes clear just how twisted and ingenious this web of crime is, D.I. Grace will realise that it may be impossible to stop it...