The seventh serial released by Nat Levine's penny-pinching but enterprising little Mascot Pictures, King of the Congo was released in three versions: silent, sound-on-disc, and sound-on-film. The latter came with several dialogue scenes, making Levine and his staff pioneers in the new art of outdoor sound filming. Veteran serial star Walter Miller and Jacqueline Logan, De Mille's Mary Magdalene of The King of Kings (1927), go in search of missing relatives in Darkest Africa. Through ten somewhat stodgily paced chapters, the two innocents battle a devious gang of ivory smugglers -- not to mention a fair amount of stock-footage wildlife -- only to discover that the man they thought was their enemy is actually Miss Logan's long-lost father and their guardian angel. The latter was played in his most menacing way by Boris Karloff, making this his third "red herring" role for Mascot.
by Hans J. Wollstein synopsis