Joanna Watson, the daughter of Sherlock Holmes, continues to pursue the espionage investigations that have recently become her specialty (A Study in Treason, 2018, etc.).
November 1915. Dr. Alexander Verner suddenly appears at 221B Baker St. with a story for the Watson family about how he was taken in a carriage with blacked-out windows to visit a patient whose identity he was not told but who managed to communicate that he was being held captive. After Dr. Verner leaves, Joanna ponders the problem together with her husband, John Jr., and her father-in-law, Holmes amanuensis Dr. John H. Watson, concluding that the unknown man is being held by German agents who may also target Dr. Verner. They arrive at Verner’s door only to find Inspector Lestrade of Scotland Yard investigating the man's disappearance. Lt. Dunn of Naval Intelligence, called to join the party, reluctantly identifies the mysterious patient as Alistair Ainsworth, a citizen who’s highly prized by German spies. Because Verner’s spilled chloroform on the floor, Toby Two, a hound with an amazingly sensitive nose, can track the odor to a deserted house where they find the body of Dr. Verner, tortured and strangled, but no sign of Ainsworth. Dunn finally acknowledges that the abduction of Ainsworth, one of four people in a top-secret cryptanalysis unit charged with making the British naval codes fail-safe, could spell disaster. Ainsworth’s fellow workers, all brilliant and unorthodox in their methods, are both suspects and sources of help in recovering him before the Germans can break him and get the sensitive information they seek. Using her father’s methods, Joanna leads the search for Ainsworth, who, despite being moved from place to place in a high-stakes game of cat and mouse, keeps hiding clues in plain sight for Joanna and her crew to follow.
Fans of all things Sherlock-ian will delight in Joanna, so like her father and already training her schoolboy son, Johnny, in the methods that have solved so many cases like this exceptionally tricky one.