The phone rings. A voice says "You have one hour to live" then hangs up. Surely, a prank? A wrong number? But someone is watching, waiting, working to take your life in one hour. The job of finding out who -- and why -- falls to DI Helen Grace, a woman with a track record in hunting killers. This time the killer seems to always be one step ahead of the police and the victims. With no motive, no leads, no clues... is Grace in over her head? .