The Three Gables

S7 E1: Isadora rejects her diplomat lover, Douglas Maberley, in favour of the young Duke of Lomond. With his life shattered, Douglas completes the manuscript of his life story and then dies in mysterious circumstances. Mary Maberley is offered a large sum of money for her house and contents and calls in Sherlock Holmes to investigate. With the theft of the manuscript, Holmes threatens to expose Isadora - but what of her engagement?