David Threlfall (Shameless, Midwinter of the Spirit) stars as DCS David Baker, who heads up the investigation into the brutal murders of two Leicestershire schoolgirls during the 1980s. Only a few miles away, Dr Alec Jeffreys, (John Simm, Doctor Who, Life on Mars) a scientist at Leicester University, invents a remarkable technique to read each individual's unique DNA fingerprint.