Rahman Khan cannot leave the police. At least not yet.

He has a new team, a new supervising officer and an old obsession - to finish what he had hoped would be his one last case - if it will let him.

Driven to find a virtual foe known only as the Stoatmaster - behind the procurement of children for wealthy and powerful paedophiles, he must first solve the riddle of the Purples.

The abyss of the dark web looms and hypnotically beckons.

Another fugitive they cannot find - this time of flesh and bones - the killer of a colleague, the sadistic terrorizer of children - an enemy who is to them incarnate evil, indivisible, inescapable, evil - and seemingly as elusive as the Stoatmaster.

They cannot find this creature - but it can find them.