 A lone aircraft drops a bomb over farmland. Nearby sheep start dying, then a farmers wife, and Sam falls ill. Then cows fall sick and mysteriously disappear. Foyle s enquiries lead him to work on biological warfare and the search for a cure for Sam, as her illness looks terminal. Meanwhile, Sgt. Milner investigates the murder of a war hero by a conscientious objector, who happens to be the brother of a past love of his.