After a rare gem is stolen from an exhibition at a posh hotel, Inspector Farraday recruits former thief Boston Blackie to retrieve the stone. Along with his assistant, 'The Runt', Blackie focuses his investigation on the hotel manager, George Daley, and his sister, Eileen. Through disguises and ruses, Blackie and the Runt trick their way to discovering the perpetrators.

Chester Morrisas Horatio 'Boston Blackie' Black
Janis Carteras Dorothy Anderson
William Wrightas Paul Martens
Richard Laneas Inspector Farraday
George E. Stoneas The Runt
Robert B. Williamsas Matt Healy
Mark Robertsas George Daley
Dorothy Maloneas Eileen Daley (Uncredited)
Joseph Crehanas Jumbo Madigan (Uncredited)
Ben Taggartas Traffic Cop (Uncredited)