A talented amateur sleuth takes on a locked-room murder in this golden age whodunit set in a gloomy, forbidding castle. Late one night the body of Mary Gregor was found in the castle stabbed to death in her bedroom - but the room was locked from within and the windows were barred. The culprit leaves only one clue, left on the floor next to Mary's body. Who's got the right theory for the murder, and can it be proven before the wrong person is arrested? This classic British mystery, first published in 1931, has enough complex plotting and red herrings to win a new generation of fans for Anthony Wynne.