Elephant's Work by Edmund Clerihew Bentley

When fed up and thoroughly peeved Chuny causes the train to crash, little does she know that her rage has sparked off a staggering chain of events involving an amnesiac who, in his quest to find a wanted criminal in order to resolve a case of mistaken identity, meets the formidable General de la Costa, learns a great deal about diamonds and becomes embroiled in an extraordinary affair involving the Bishop of Glasminster's mitre. This classic 'shocker' was written at the suggestion of Bentley's friend, John Buchan.