When Professor Squawkencluck's Seriousizer ray is nabbed by Pompom, the fun and laughter-hating president of the clown planet of Bozoria, Danger Mouse teams up with his clown-shaped Bozorian equivalent, Cupcake, in order foil whatever dastardly plan is afoot. As it turns out, Pompom intends to use the ray to strip Bozoria of all things amusing, and he kidnaps Squawkencluck and exploits her extreme fear of clowns to coerce her into unlocking the Seriousizer's technology.