How to Snoop in Your Sister’s Diary by Janet Adele Bloss, 1989.

Lately, Haley has been jealous because her older sister, Lauren, has a new boyfriend and is spending all of her time with him. Haley feels neglected because Lauren doesn’t want to spend time with her any more. Haley resents the new boyfriend and worries about what Lauren and her boyfriend are doing together, so she begins regularly snoops in her sister’s diary to learn the details of Lauren’s relationship with her boyfriend.

However, Haley soon reads something shocking in her sister’s diary. Lauren might be about to do something disturbing and dangerous. But, what can Haley do about it when she wasn’t even supposed to know anything about it? If she reveals what she knows, Lauren will know about her snooping.

It turns out that Lauren already knows about the snooping and is angry with Haley about violating her privacy. Lauren isn’t actually doing anything wrong or even thinking about doing something wrong. She only wrote the shocking section in her diary to scare Haley, sort of like proving the old saying about how people who eavesdrop might hear things that they wish they wouldn’t (although the original saying is about how eavesdroppers might hear bad things about themselves). When Haley finally goes to plead with Lauren not to do what she thinks Lauren is about to do, Lauren reveals the truth, and the girls have an honest talk about what’s really been happening between them.

Personally, I didn’t think that the characters in the book acted in a very realistic manner. The main character didn’t react to certain situations in the way I would have expected, given her age. This is one of those stories which depends on characters holding things back and not communicating with each other openly for much of the story because, if they did, the story would have been resolved right away.