Just finished "Hamlet, Revenge!", by Michael Innes, which is the second book in his "Inspector Appleby" series of detective novels. Appleby is called in to investigate when the Lord Chancellor of England is murdered while taking part in an amateur production of "Hamlet" at an English country house. This is a very long and complex, but extremely satisfying, detective story in the best tradition of the "golden age" of English detective fiction. The best crime novel I've read in a very long time, and I thoroughly recommend it. It was voted #68 in the Crime Writers' Association
Top 100 Crime Novels of All Time (which would, in itself, be a worthwhile reading challenge for someone).