Only when her mother has bled to death on her bedroom carpet is six-year-old Keisha Adams allowed to look away. It is then the man takes the knife away from her throat and speaks: 'Embrace your pain, for it is the breaking of the shell that encloses your understanding.'

The killer strikes daily, forcing his random victims' loved ones to watch his butchery before assuring them someday they will thank him. And then, as mysteriously as he had appeared, he vanishes, leaving no trace of his existence.

With one week until her wedding day, and with a demon from her past back to haunt her, troubled DCI Catherine Jessop doesn't need such a big case. In all her years hunting the sick and twisted she has never known such a prolific and elusive killer. All she knows about him is that he has a sadistic lesson to teach about salvation through suffering, and that he cannot be found.

But when she learns of her quarry's chilling past, and that she and her family may be his next pupils, her life is thrown into a living hell of paranoia and self-doubt. She fears she will not be able to stop him. And she may be right.

Because his final lesson is beyond anything she could have imagined... A lesson so shocking it will change the lives of millions of people forever.