ILLUSTRATIONS[ The gem lay between them, a splash of crimson flame . . . Frontispiece ][ Diagram of second floor ][ The door opened a few inches, to reveal the figure of Alexander Burke ][ Cipher ][ Cipher (repeated) ][ "I'll shoot," she announced in a tense tone, "so help me, I'll shoot" ][ "Uncle, Uncle, sit up! Don't go to pieces this way" ][ Cipher (repeated) ]