Minneapolis Simpkins--her odd name is never explained--wants a pet, but Mom says no. The trouble starts when Minn brings home a little monster she finds crying in the rain. She hides it in the basement and spends a frantic dinner hour trying to keep the knowledge from her mother--as the monster thumps about, eats all their stored apples and potatoes (whole), and thereupon grows bigger and bigger. Mom never does catch on--in fact she takes Minn's ultimate confession for wistful fantasy--but the episode does persuade her to go out and buy two kittens. Funnier and more empathic picture books have been based on the desire for a pet, but this will do for about one reading, thanks to the changes rung by the monster's troublesome antics and Minn's cover-up tactics.