Mary Anne Spier's stepsister, Dawn, arrives for a visit, bringing along a friend, Sunny, who is trying to cope with her mother's death, a situation Mary Anne had once been through herself.

Mary Anne and Stacey are in Sea City working as mother's helpers for the Pike family. When each of the girls meets up with her boyfriend from last summer, things start to get complicated.

The rest of the Baby-sitters are shocked when Mary Anne, tired of being a plain Jane, gets a chic new haircut and a new wardrobe, and their reaction enrages the excited Mary Anne.

Trying to help her hard-working father and twin sister to adjust to life in Stoneybrook, Abby Stevenson becomes the newest member of the Baby-sitters Club and shares her first adventure.

Stacey's parents are getting a divorce. Stacey is sad and angry, and she has a big decision to make--stay in New York with her father, or move back to Stoneybrook with her mother.

Even though Cokie has never been nice to Mary Anne, Mary Anne has always been nice to Cokie. But this time Cokie's gone too far--and Mary Anne is going for revenge, with a little help from her friends.

Mary Anne's been going through some big changes lately, but when a friend who's facing her own difficulties comes to stay for the summer, can Mary Anne help her cope?