To his friends, his foes and even to himself it looks as though Tom Thorne's career is on the skids. On his last case he had seriously over-stepped the mark, and now gardening leave has been suggested and all he has to tend is a window box. So when it appears someone is targeting London's homeless community it seems pefectly natural for Thorne to take a step nearer to the gutter and go undercover amongst them. He blends into the sometimes invisble community easily - too easily perhaps - but the information he gleans quickly proves that this is no random killer, it is someone with a very distinct purpose and a very specific list of victims, only the team supporting Thorne from the outside don't have the key to motive or identity. Then somehow the fact that a policeman is working under cover becomes public knowledge.