A beloved aristocrat accused of theft. A beautiful bride in deadly danger. And unless Holmes and Lucy can stop a killer, a grand historical gala will be forever haunted by a grim and ghastly murder. London, 1900—Sherlock, Lucy, and the Baker Street team are called to investigate Sir Galahad Trent, a popular local aristocrat whose castle restoration should be the pride of the local community. But is Galahad the benevolent medieval enthusiast that he seems? Detectives from the Pinkerton's agency suspect he has stolen two million dollars in bonds from the United States Treasury. His wife, Lady Carlotta, a 'dollar duchess' whose dowry funds are running low after a year of Galahad's profligate spending, may face impending peril. Her American father claims that Galahad is seeking yet another million-dollar dowry and is about to kill Lady Carlotta. A gala dedication ceremony promises financial support for a rebuilt castle, as well as bright pageantry and festive merrymaking. But then the loan to fund the castle restoration project is placed in jeopardy when Galahad's banker is found dead, stabbed with a medieval dagger. Galahad insists on going forward. But then another murder is discovered, Lady Carlotta's father goes missing, and Flynn and Becky are set upon by an unknown assailant, and imprisoned. Can the Baker Street team thwart a murderer's sinister scheme? Or will the daring detectives be defeated by the devilish cunning of a dastardly evildoer?