Farmer John Tatton and his son Alfred do not get on, John accusing the boy of being a useless drunk like his late mother. Alfred confronts the family doctor Adam Crawford, taunting him for having a much younger wife Oona, who has just confided in Mrs McCarthy that she is pregnant. Alfred is found dead, mangled in farm machinery and soon afterwards anonymous letters appear, accusing Dr Crawford of the crime as Oona was supposedly having an affair with the dead man - something she denies. Dr Crawford confesses to the murder of Alfred but Father Brown knows better and seeks out the truth.