An oriental mad scientist has invented a mystery ray gun. He tells Droopy and Barney Bear to guard it from people. Droopy must protect it from falling into the wrong hands by using a rather unusual method: a Jekyll and Hyde formula. Slick Wolf tries to steal it, but Droopy keeps turning into a large monster, who then beats him up. Droopy frees himself and Barney from Slick's trap, and chases Slick away.