Plot synopsis: In 1921, Major Herbert Rowse Armstrong, a solicitor and magistrate's clerk living in the small Welsh town of Hay-on-Wye, was arrested. Charged with poisoning his domineering wife, Catherine, and later attempting to poison a business rival, Oswald Martin, by administering arsenic to them, Armstrong claimed at trial that he had bought the arsenic simply to kill the dandelions on his lawn.