The Cheetah is on the hunt in the Gotham City Natural History Museum. She pounces on her prize, an ancient necklace fabled to grant its wearer incredible power. Later that night, when Batgirl and Supergirl respond to the burglary, they discover that the legend is true. The necklace gave the Super-Villain power... and mutated her into a mindless monster! Can the Super Heroes unearth the secret to undoing the midnight mutant madness?