In the latest installment of this acclaimed series, Sherlock Holmes's daughter faces an elaborate mystery that threatens the second most powerful man in His Majesty's government. His position is such that he answers only to the king and the prime minister.

In 1918, during the height of the Great War, Joanna Holmes and the Watsons receive a late-night, clandestine visit from Sir William Radcliffe, the Chancellor of the Exchequer, who brings with him an agonizing tale of blackmail; a case so sensitive that it can only be spoken of in the confines of 221B Baker Street.

An unknown individual has come into possession of salacious photographs, which not only sullies the family name, but may force the chancellor to vacate his seat on the War Council where his advice is most needed. The blackmailer has in their possession revealing photographs that show Sir William's granddaughter in romantic encounters with a man other than the aristocrat to whom she is engaged to marry. Should the pictures be released to the public, the wedding would be immediately called off, and the prospect of the granddaughter ever finding a suitable husband would vanish.

Sir William's family has been forced to pay exorbitant sums for several of the photographs, but even more salacious pictures remain in the blackmailer's possession--and will no doubt carry greater demands and threats. Scotland Yard cannot be involved, for fear of public disclosure. It thus falls on the shoulders of Joanna and the Watsons to expose the blackmailer and procure the photographs before irreparable harm comes to the chancellor and his family.