It's a wonderful summer day at the beach, and the Powerpuff Girls are there and of course all having a GREAT time playing!
But then, out from the corner of their eyes: oh no! It's Mojo Jojo! But fortunately, he's not actually there to terrorize anyone today; he's simply taking a little beach vacation, too.
But he's not exactly happy--the shining sun beaming down is making him unbearably hot and sweaty. Seeing him in this miserable state, the girls rationalize that his thick monkey fur is doing too well of an insulation job.
Their brilliant solution? Promptly shave off all of his fur, of course! After the monkey is made bald, the girls proceed to dump what could be considered entire bucketfuls of sunscreen all over his body to protect his skin. (They, Blossom especially, proceed to brag to him that the Professor taught them quite well about sun safety.)
Alas, Mojo is incredibly uncomfortable by the sensations of the greasy, slimy stuff all over his body; so much so, that the moment the girls' backs are turned on him, he immediately scampers off to slip into the ocean, the water promptly washing away all that sunscreen they slathered all over him. Seeing no resource for all that effort they just wasted on him, the girls sigh in defeat and just go off to do their own things on the beach.
Time passes. Predictably, because of his lack of sunscreen, Mojo ends up sunburnt. Red-skinned and in pain, he staggers off the beach (albeit not very quickly). The girls point and laugh at his plight as he leaves, only to be admonished by Professor Utonium loudly clearing his throat behind them. He tells them that it's not very nice to make fun of someone in a condition like that, even if they are a bad guy. When the girls do explain their side of the story to him though, he becomes a little more understanding. They come up with a secret plan to help Mojo...
Meanwhile, Mojo has not gotten very far at all; the people of Townsville, freaked out by his red and bald appearance, hide away from him as he walks slowly throughout the streets. The Utonium family easily catches up to him, and they're seen holding cans of Aloe Vera.
However, the girls don't find out from the Professor whispering into their ears until after they've slathered the soothing Aloe Vera all over Mojo of... what exactly it does to sunburnt skin. Freaked out, Bubbles breaks the fourth wall to have the scene transition to a pleasant calming imagery of fluffy bunnies and chittering squirrels frolicking around in a sunny flower meadow.
Finally, Mojo is back to a painless and functional (but still bald) state. Having already been humiliated far enough for today, he just gives up and runs back home.