While visiting New York, Grand Duke Ludwig finds his bank account frozen owing to a dispute with the German government. Desperate for money, the nobleman undertakes a job for newfound friend Gordon, a jewel thief posing as a millionaire. The hapless Ludwig is tricked into using his good name to facilitate the theft of a valuable black pearl from a prominent jeweler. Angela, a pretty young employee of the gem merchant, realizes the Grand Duke has been duped and tries to help him recover the pearl before the police close in.
A former playwright who began crafting scenarios in 1914 for Pearl White's The Perils of Pauline, George B. Seitz worked almost exclusively on Pathe serials until 1925, when he started writing and directing feature films on a freelance basis. Like many silent-era filmmakers, he toiled for independent producers on Poverty Row during the early days of talkies. When filling key roles in The Case of the Black Pearl (originally released as Sally of the Subway) Seitz cast former Pathe cronies William Burt, Harry Semels, John Webb Dillon, and Jack Mulhall, the star of his 1924 cliffhanger, Into the Net.