As Superman and Batman take Stargirl on a ride-along to protect the United Nations from Gorilla Grodd and his army of gorillas, Mister Mxyzptlk pops up from the 5th Dimension and thinks it would be great fun to put each of the superheroes' brains into another hero's body. Even when the Justice League's bravo team and Firestorm arrive and fall for the same brain-swapping move, the Justice League must find a way to trick Mister Mxyzptlk into saying his name backwards and defeat Gorilla Grodd.
