Randy O'Rourke invents a "Ditto Box," a machine that copies whatever he puts inside. When he wants a ball glove like his friend Jake's, he puts in the glove, and Zap--a duplicate for himself. If Randy and Jake want pizza, he orders one, makes a copy, and they eat two. Randy copies homework, games, and even Asthma, Jake's furry mutt. Everything is going great until his little sister wants a playmate. Twozy, as Suzy names her "twin," looks and whines just like Suzy. Mom and Dad are mad at Randy for doubling their trouble, and he has to baby-sit more girls more often. Two sisters are twice as bad! How can he get rid of the new one?