Well-to-do Chicagoan, Larry Darrell, breaks off his engagement to Isabel and travels the world seeking enlightenment, eventually finding his guru India. Isabel marries Gray, and following the crash of 1929, is invited to live in Paris with her rich, social climbing, Uncle Elliot. During a sojurn there, Larry, having attained his goal, is reunited with Isabel. While slumming one night Larry, Isabel and company are shocked to discover Sophie, a friend from Chicago. Having lost her husband and child in a tragic accident, Sophie is living the low-life with the help of drugs an abusive brute. Larry tries to rehabilitate her, but his efforts are sabotaged by Isabel who has tried in vain to reignite Larry’s interest in her.

Holmes is hired by Roland Carstairs to prevent the theft of the Star of Rhodesia, an enormous diamond owned by Carstairs’ mother, Lady Margaret. Believing the diamond will be stolen on a train trip from London to Edinburgh, Holmes deftly switches diamonds with Lady Margaret while in her compartment. Soon after, Roland is murdered and the fake diamond is stolen. Red herrings abound as Holmes, aided by Dr. Watson and Inspector Lestrade, discover the murderer’s hiding place and deduce that long-time foe Moriarty’s henchman Colonel Sebastian Moran is somehow involved in the crime.