Herbert Rowse Armstrong went down in history as The Hay Poisoner. Convicted in 1922 of murdering his wife with arsenic, he was the first and only solicitor to be hanged in the UK. But was he guilty? Was he a cunning poisoner, or was he a grieving husband wrongly accused? Much of the evidence against Armstrong was circumstantial and the scientific testimony remains disputed. In this episode we examine both sides of the case and ask whether the British justice system made a terrible mistake.