Therein lies the daunting challenge for the author. They have created a seemingly impossible crime — and now they have to solve it. Poe cracked his case with (spoiler alert!) an orangutan that escaped through a window. In Sir Arthur Conan Doyle’s “The Speckled Band,” the culprit, as deduced by Sherlock Holmes, is a deadly snake that slithered down the bell pull. Agatha Christie, the queen of the locked room, did it with great panache and sleight of hand in “Murder on the Orient Express” by misdirecting the reader into believing there was just one murderer.