Watford

In 2000 a young woman is stabbed to death while walking her dog in a picturesque park in the town. She's a twin, a woman known in her local area. A suspect is seen running semi-naked across the M1 motorway and makes his escape. Cops initially suspect the killer of Rachel Nickel might be responsible...and it takes detectives weeks to identify the real killer is a local man called Leon Amos. They find out his family are known criminals, who have been covering Leon's tracks, and that the killer may have mistakenly carried out an act of retribution on the wrong twin.