Just suppose John Buchan had decided to confront Richard Hannay with a locked room mystery. It's quite possible that the result might have finished up resembling Three Dead, One Hurt..., one of two crime novels published by Scobie Mackenzie. It was first published by Eyre and Spottiswoode in 1934 and I'm not aware that it's been reprinted since then.
There's even a Hannayish vibe to the opening scene. The first words are: 'We met on the train, Francesca and I, though of course I didn't know at that time she was Francesca'. She is a beautiful and enigmatic woman and the narrator is immediately smitten. Alas, before the train has reached its destination, he discovers that she is involved with a man called Johnny Brown.
The narrator is travelling to a remote Scottish island, which he has inherited from his late uncle (who was a crime buff with an impressive library of crime books, a fact which pleasingly proves relevant as the story unfolds). He is greeted by his late uncle's factor, a chap called Peter Brook, who is also obsessed by a woman, his estranged wife, about whom he can't stop talking.
Before long, an incident at sea results in Francesca and an assortment of strange fellow passengers coming ashore and the scene is set for an interesting and unorthodox mystery. I learned of this book from the late Bob Adey, who mentions it in Locked Room Murders, and I'm delighted to have read it at last. Mackenzie was an interesting writer (sometimes confused with a New Zealander who had the same name) and his career in the genre proved regrettably short, but this story - despite one or two oddities - is a notch or two above many others that were being written at the time.