Who Killed Cock Robin?

Dr Burgess, on his way home from a party at the glamorous Francesca Ward's riding school, knocks a stranger down in the road at Newton Magna, and the stranger mysteriously vanishes. Barnaby identifies the missing man as Sean O'Connell, a disgraced Irish vet, then he recognizes the village's new squire as Melvyn Stockard, a retired villain. A body found in a well proves to be the father of the man Stockard's daughter is about to marry... everyone knows he was against the marriage, but is Stockard a killer, and where does the missing Irishman fit in?