The Third Person by Steve Mosby
'This isn't some kind of 'dear John' letter. I'm coming back again' But Amy Sinclair didn't come back. That note on the kitchen table was the last that her boyfriend, Jason, heard of her. At first, he had let her have her space but as the weeks turned to months the worries had set in...and eventually he went after her. What he found appalled him. It seems that Amy had had a secret life on the internet and had met some people she shouldn't have. And one of them took her. Now Jason sits at home and cruises the same horrific websites that she once walked through to find her kidnapper. But when he lays a trap for a monster that he meets in a chat-room he gets more than he bargained for. He finds that nothing in this story is as it seems and that the clues lie in the mistakes of his own past...