Perfect Prey

In the midst of a rock festival, a charity worker is murdered. The following week, the body of a school teacher is found in a dumpster. DI Ava Turner and DI Luc Callanach have no motive and no leads, until words describing each victim appear graffitied onto buildings. It's only when they realise the words are appearing before the murders, that they understand the killer is announcing his next victim.