Veteran street performer Charles (Charles Laughton) takes petty thief Libby (Vivien Leigh) under his wing. Together they create a new "turn" (routine) for Charles's troop of "buskers" (street performers). The "buskers" specialize in entertaining the crowds waiting to enter the legitimate "theatres" (theaters) of London's West End. Libby's talent is recognized by songwriter Prentiss (Rex Harrison) and her ambition causes her to leave lovelorn Charles in the lurch. She is successful while Charles descends into the gutter.
St. Martins Lane was released in London in 1938 but was released as Sidewalks of London in the U.S. in 1940. According to Robert Osborne of TCM, the American distributor decided to wait until after Gone With the Wind was released to capitalize on Vivien Leigh's newfound fame.