The Traitor's Gate

It's the ultimate plot to steal the Crown Jewels from the Tower of London. But when a criminal mastermind finds Scotland Yard detectives sniffing around his tracks, things become far from easy.
Hope Joyner, ward of a Mr. Hallet whom she has never met, is in love with Sir Richard Hallowell. Diana Montague, who was once engaged to Sir Richard, now keeps very dubious company - Sir Richard's brother Graham for one. He has just been released from prison. Since Graham has been away Diana has acquired money, and she is now Press Secretary for the Prince of Kishlastan, who according to Colly Warrington, is totally besotted with her...
Edgar Wallace has woven a story that is distinctly superior to the general run of mystery yarns.