The Kentish Manor Murders — Julian Symons

What the Haynes encounter at Castle Baskerville is, in Val's words “really screwy.” A tycoon apparently allergic to light surrounded by moats and drawbridges and a permanent staff of guards, doctors, nurses and “companions: who work under the directions of a “prime minister.” Despite all this Sheridan agrees to do the performance and leaves for another appointment in Europe while Castle Baskerville is prepared for the great event.

In Copenhagen Sher encounters events Val would also describe as screwy; a meeting with Bertie Bailey, vaguely remembered from school and Oxford but who claims close friendship with Sher; a proposed introduction to a friend of Bailey's who never turns up; another meeting with a Professor of Sherlock Holmes Studies who asks Sher's opinion on a manuscript of an unpublished Conan Doyle novel; the murder of Bertie Bailey hours after Sher had last seen him.