Then they hang up. Surely, a prank? A mistake? A wrong number? Anything but the chilling truth... That someone is watching, waiting, ready to take your life in one hour.

But why?The job of finding out falls to DI Helen Grace: a woman with a track record in hunting killers. However, this is one case where the killer seems to always be one step ahead of the police and the victims. With no motive, no leads, no clues - nothing but pure fear - an hour can last a lifetime...