Babysitter III, The (Point Horror) by R.L. Stine - Vintage Paperback

Bad company...

Jenny just wants to forget the man who murdered all the baby-sitters. The man who almost murdered her. He's dead now. And Jenny's gone to visit her cousin Debra. But Debra has a babysitting job. And now she's getting those phone calls, too. Just like the ones Jenny used to get:

Hi, Babes. I'm back. Company's coming...