How well do you REALLY know your neighbours? RIGHT NOW around 600 unconvicted murderers are living quiet respectable lives in Britain. Killers like Ian Lowther who married, brought up a daughter and led a law-abiding life in the 23 years after brutally murdering Mary Gregson. Men who, in the past, could have relaxed in the certain knowledge that they would never be caught. When the police finally came for Lowther at his house overlooking the very canal where he murdered Gregson, it wasn't due to a tip-off or confession - it was a scientific breakthrough. This remarkable case is not unique. In the 10 years since the discovery and development of DNA testing, fragments of evidence dating from past decades have been brought out of police store rooms, dusted down and tested. Samples like the one that caught Lowther - a tiny spec lying at the bottom of the Leeds to Liverpool canal with Gregson's body - were brought back to life to finger the killers. This is the story of how those breakthroughs changed the face of the world. It is the story of DNA and the race to bring down some of Britain's most evil criminals.