It's all change for Kembleford. Not only is there the opening of a new model village, the labour of love for Peter Mossop and his best friend Joe Telford, but a property developer is proposing to build a new housing estate in the village. The planned vote on the development has torn apart siblings Brendan and Scarlett Streatham, whose late father owned the land. Father Brown is kept busy interviewing a new secretary following Mrs McCarthy's departure – he's torn between the orderly Mrs Burns and the enthusiastic Mrs Devine. He becomes distracted from this task to investigate the murder of Joe, who is found stabbed to death whilst walking his dog. When Peter's wife, Jennifer Mossop is also found dead, Father Brown realises the model village is being used by the murderer to plan their attacks.
