Things are quiet at the Hall of Justice with no major calamities for the SuperFriends to deal with. Elsewhere, at that moment, Zan and Jayna are watching construction of an office tower and Gleek finds a large red rock. The Wonder Twins bring the rock back to the Hall of Justice and Superman recoils in terror upon seeing it. Samurai explains to the twins that the rock is actually red kryptonite, which has unpredictable effects on Superman. A moment or so later, the SuperFriends see Superman regress to the size and mind of a child, who fusses almost immediately that he wants better clothes.
The SuperFriends try to contain the Superbrat's damage but the extra dimensional imp Mxyzptlk appears and complicates things. To appease Superbrat, Mxyzptlk transforms Samurai into a basketball, Firestorm, Zan and Jayna into wind-up dolls and Gleek into a toy monkey. Mxyzptlk and Superbrat teleport away and the SuperFriends return to normal and set off to stop Mxyzptlk from creating havoc.
The heroes head to the city zoo and Mxyzptlk uses his powers to release the zoo animals that head towards downtown Metropolis. The SuperFriends manage to recapture the animals before any harm occurs.
Mxyzptlk deals with Superbrat's hunger by conjuring up large amounts of food and Firestorm uses his powers to avert a water tower toppling from Superbrat's tantrum. Mxyzptlk conjures up a gigantic mound of ice cream for Superbrat and Samurai uses his whirlwind power to whip the food into whipped cream to prevent a passing monorail from crashing into a hard substance.
Mxyzptlk takes Superbrat to the local stadium where Mxyzptlk uses his powers to hurl boulders that Superbrat clubs into the sky with an oversized bat. Firestorm uses his powers to transform the boulders into balloons before they hit a passing airplane. The SuperFriends arrive in the stadium and Mxyzptlk mocks them to the point that he uses his powers to have spectators holding up signs that spell out a cheering message for the imp. Samurai subtly uses his whirlwind powers to reverse the letters and when Mxyzptlk reads it again, the imp disappears back to his home dimension. The next day, Superman wakes up normal sized but finds his costume seems to have shrunk and the other SuperFriends asleep after an exhausting day.