A late Gideon Fell book, published 1958, just a few years before Who's Afraid of Virginia Woolf. It starts off as a midcentury American small town novel about academics with unhappy marriages, and then we get the locked room mystery. The mystery itself is inspired by a (fictional) unwritten Wilkie Collins novel, including letters from Collins to Dickens hinting at the clever trick.
It's a long novel with no single central character, but with several interlocking and overlapping storylines. It's carefully plotted, and the different storylines and groups of characters mesh together like gears.
This is also one of the books that reminds you that Dickens can be very funny, and sometimes it's the most horrible characters who are the funniest. My favorites are probably the two fortune-hunting swindlers who married each other because each of them mistakenly thought they were marrying money. The first passage that literally made me laugh out loud was when “that horrible old Lady Tippins (relict of the late Sir Thomas Tippins, knighted in mistake for somebody else by His Majesty King George the Third, who, while performing the ceremony, was graciously pleased to observe, “What, what, what? Who, who, who? Why, why, why?’) begins to be dyed and varnished for the interesting occasion.”
It begins with someone stealing hats and putting them in whimsical places, then we get the theft of an Edgar Allan Poe, then a murder. Yes, all is connected.