It is past midnight when two callers come knocking at the London flat of down-and-out, long-out-of-work Peter Diamond. When they turn out to be two CID men from his former police division of Avon and Somerset, he's baffled. When they order him to accompany them, he's mad as hell at being rousted from his warm bed - and intrigued. When it turns out his old department has an emergency only he can handle, he can barely stop himself from saying "I told you so.".

John Mountjoy, a woman-hating murderer Diamond arrested four years earlier has broken out of prison and taken a CID officer's daughter hostage. His demand is to talk to Peter Diamond. His reason? He wants Diamond to clear his name, insisting he never brutally stabbed a beautiful reporter to death and filled her mouth with roses as a macabre touch. But he will kill the hostage, unless Diamond gets the proof to overturn his conviction.

Does this mean Diamond will be an official CID man again? With even his old enemies in the precinct welcoming his assistance, Diamond is in the cat-bird's seat if he can pull off what seems impossible: to follow an old, very cold trail and miraculously come up with a new killer. Now, with time running out, Diamond will either fall flat on his face - or prove his real worth. Pure 10 carat genius. The real thing. A Diamond of outstanding detection.