Wally Featherby loves animals. He has several pets, including a frog, a tarantula, a hedgehog named Mimi, and a parrot named Golly. But one day while teaching Golly to say Mimi's name, something strange happens. His family starts claiming to see Mimi all over the house, even though she's still in his room. Wally's friend, Axado, even calls to say Mimi is in her yard. When the friends investigate the mystery, they discover hundreds of hedgehogs overrunning the city! What's going on? What's causing the multiplying Mimis? And how will Wally and Axado stop the hedgehog horde?