Mother's Helper — A. Bates

Becky gets to spend the whole summer on a beautiful island, babysitting one little boy who is no trouble at all. It's a dream job. There's even a possible romance developing with the boy next door. Her employer is one strange lady who doesn't seem to have a clue how to care for her own child, but that's what she hired Becky for. Besides, she's not around much so it's not much of a problem. But the phone calls that ring and ring behind a locked door are a problem, and the accidents that no one really believes are accidental, and the rumors of who might be responsible for them. It's not that easy to escape from an island if you don't have a boat and are afraid of the water. Becky is stuck where she is, with a boss and a maybe boyfriend she can't completely trust. But she's going to have to trust someone, so she will have to choose between them if she wants to survive the summer.