When Petronella Morton puts an ad in the local newspaper for "MONSTER-SITTING AFTER SCHOOL AND WEEKEND'S, "little does she know that her phone will begin to ring…AND RING AND RING AND RING! Nelly soon discovers that there are families of monsters living secretly all over the Montelimar Estate! Whether it's trying to keep Slop the Squurm entertained, walking the Grerks' pedigree gog, Glug, or solving a bank robbery with the help of three little Water Greeps, Nelly's always got her hands full! Join her at three different addresses, for three monstrously different monster-sitting adventures!