Children's mystery book. Better than I expected. ( )

Beth keeps getting paranoid about the house next door to the house she's moved into, but she keeps telling herself there are reasonable explanations. If only she could figure out what they are! She's also lonely and friendless in her new town while she waits for school to start. In the house where she's cat-sitting, cats are getting in and out, doors are opened and closed, things are moved around, and she can't figure out how it's all happening. Finally she finds out a local boy was also hired for cat sitting and she makes a friend. ( )

A cat sitter goes missing.