The Lost Gallows, by John Dickson Carr

 9780712353632British Library, 2020256 pppaperback(read earlier)In this installment of the Bencolin series, Carr offers up a bit of detective fun that blends British lore, a bit of  Egyptian flair and an intriguing mystery from the past, all of which together make for a crafty whodunit.   Bencolin and Marle are in London to see a play, and there they are staying with one of Bencolin's old friends