An antiquarian book dealer has been stabbed to death. There are no suspects or witnesses. Can the police find his killer? And what's happened to his £50,000 early edition of Wind in the Willows?

Cameras follow Thames Valley Police's investigation into the murder of 64-year-old Hang Yin Leung, who died after being violently assaulted during a burglary at her Milton Keynes home in January 2017. Filmed over 12 months, the programme interweaves the police's enquiries with an intimate portrait of a British-Chinese family coming to terms with the impact of murder, with the story of migrants from Hong Kong who came to the UK in search of a better life for their son unfolding alongside the hunt for the killers.