Complex sentence: He protects Libby, Vivien Leigh, a runaway/pickpocket/dancer/busker, when she steals a gold cigarette case from successful song writer Harley Prentiss, Rex Harrison; and, takes her into their troupe, making their trio into a quartet.
Split into simpler sentences: He protects Libby, Vivien Leigh, a runaway/pickpocket/dancer/busker, when she steals a gold cigarette case from successful song writer Harley Prentiss (Rex Harrison). He then takes her into their troupe, making their trio into a quartet.