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Clark (George Reeves) accompanies Lois (Phyllis Coates) to her home town of Clifton-by-the-Sea, a fogbound community which is apparently being terrorized by a sea monster. It soon develops that the "monster" is merely a ruse to enable a number of disreputable locals to cash in on the recent discovery of "hydrozite", a secret ingredient vital to the creation of the hydrogen bomb. This is one of the most violent and horrifying Superman episodes ever filmed--even an innocent dog gets killed!