After threatening to expose secrets of other parents at Midsomer Pastures school single mum Debbie Moffett is lured by a phone call to her death in the dairy where she worked. She had been having an affair with Oliver Ordish,whose wife Beatrix was chair of the school's PTA,and when he too is killed Beatrix is the prime suspect. Greg Brantner,whose wife Hayley inherited the dairy from her late father, had worked with Debbie to streamline it,antagonizing local farmer Helen Caxton and her brother-in-law,dairyman Jim Caxton. Further deaths suggest dairy politics are the motive until Barnaby discovers that several of the suspects and victims had been contemporaries as pupils at Midsomer Pastures. He must find out which one was schooled in murder.