(W) Ann M. Martin, Arley Nopra (A) Arley Nopra. Mallory knows she's a good baby-sitter. She's been looking after her seven younger brothers and sisters for years. So when Kristy offers her a steady job baby-sitting for the Arnold twins* Mal thinks it'll be easy money. The twins sure are cute in their matching outfits. But once Mrs. Arnold leaves* Marilyn and Carolyn turn into twin terrors! They trick Mallory so that she can't tell them apart and they act like spoiled brats. Taking care of Marilyn and Carolyn is a baby-sitting nightmare. But Mallory is a responsible member of the Baby-sitters Club and she's not giving up!