In early 1925, the Honourable Daisy Dalrymple Fletcher, recent mother of twins, resumes her journalistic career by agreeing to write a piece about the Tower of London - the Bloody Tower - for an American magazine. Invited to observe the centuries old ritual Ceremony of the Keys, she's spending the night (her first time away from her babies) since the complex is locked and guarded, and the high walls are surrounded by a disused moat. Having been given a tour of the Crown Jewels, interviewed and observed the Yeoman Warders, and met the Ravenmaster, Daisy has more than enough material for her article and decides to leave as early as possible the next morning to return to her family. But when walking down the stairs, she almost trips over the dead body of one of the Yeoman Warders.
