Cyril Twyford

A card cheat is threatened with exposure into joining a criminal enterprise that Sherlock Holmes believes is controlled by Professor Moriarity.

Holmes goes on the trail of a Rembrandt painting, stolen by a drug-addicted artist.

The young Lord Sloane marries a musical comedy actress, much to his parents' disappointment. The actress's brother-in-law gets into betting difficulties so she obtains money from her husband to help him.

Jewel thieves kill a rich widow and frame a fake medium.

In Dijon, Inspector Hanaud investigates Betty Harlowe after her uncle, Boris Waberski, accuses her of poisoning her wealthy aunt for an inheritance. While an initial autopsy finds nothing, Hanaud discovers the use of Strophanthus Hispidus—a rare, undetectable poison applied via an antique arrow. Amidst a flurry of "poison pen" letters and deception, Hanaud proves the murder occurred despite the lack of conventional medical evidence.