There are two big things to know as we start this book: Dawn’s mother and Mary Anne’s father have been going on a ton of dates and are exclusively dating each other, and Mary Anne has just picked up a fairly steady sitting job with the Arnold twins, Marilyn and Carolyn.
Mary Anne soon finds that there’s trouble brewing between the twins. Since Mallory started baby-sitting for them, they’ve become much more independent, but they might have gotten a little too independent for Marilyn’s liking. She’s hurt that Carolyn is off hanging out with her friends (Haley Braddock, Vanessa Pike) because Marilyn doesn’t have any friends. Well, she tells Mary Anne that she has a foreign friend named Gozzie Kunka (!!!) who has traveled the world. That sounds fake, but okay. When Carolyn comes home, there’s mad tension between the twins. Marilyn thinks Carolyn and her friends are snobs and Carolyn is defensive. (Marilyn is probably just jealous because she only has one friend who is probably fake.) Carolyn, Haley, Vanessa, and Charlotte Johanssen want to start an exclusive club of girls and Marilyn is immediately left out. But when Jessi is baby-sitting for Haley and Carolyn, Carolyn mentions that Marilyn never plays with her anymore and she’s “too bossy” (Kristy Junior?)… so the twins certainly have different perspectives about what’s going on.
Mary Anne and her father invite Dawn over for dinner, and Mr. Spier tells the girls he wants to surprise Mrs. Schafer for her birthday. He’d have her meet the three of them at a restaurant. The girls are excited, but they get into a little fight when Mary Anne is trying to think of presents for Mrs. Schafer. They get over it quickly, though. Marilyn and Carolyn, on the other hand, don’t get over their fight quickly. Marilyn is upset because she feels like Carolyn leaves her out and that their mom likes smart and outgoing Carolyn better; Carolyn is upset because Marilyn was bossing her friends around and feels like their dad likes musically talented Marilyn better. At one point they use masking tape to make a line down the center of their bedroom (so cliché). (Also – foreshadowing!) Mary Anne doesn’t know what to do.
At Mrs. Schafer’s birthday dinner, Mr. Spier pulls out all the stops – including buying Mrs. Schafer a diamond engagement ring. The pair announces to Mary Anne and Dawn that they’re getting married – soon! Mary Anne and Dawn are shocked and then realize they’re going to be stepsisters. Exciting! There are a few things that worry Mary Anne, though – Dawn seemed jealous of Mrs. Schafer’s reaction to Mary Anne’s thoughtful birthday gift; Mrs. Schafer doesn’t like cats and Mary Anne refuses to give up Tigger; Mr. Spier is neat and tidy and Mrs. Schafer is disorganized and messy – how are they going to live together? Mostly, though, Mary Anne is thrilled to finally have a big family on the way, and especially that one of her best friends will be her stepsister!
She and Dawn break the news at the next BSC meeting and everyone is ecstatic for them. Mary Anne knows, though, that Kristy will feel hurt and a little left out now that Mary Anne and Dawn will have this special lifelong bond, so Mary Anne slips her a sweet note:
Mary Anne and Dawn’s parents break their hearts a little bit by telling them they don’t really want to have a wedding – and certainly not the big fancy wedding Dawn and Mary Anne have dreamed up. They want something very small and simple – a short ceremony and then a family dinner. Mary Anne and Dawn manage to talk them into something a little bigger, so the BSC and Dawn’s grandparents can come, and their parents agree. The girls are excited again – they’re going to be stepsisters. But Mary Anne is less excited when she finds out that she and her father will be moving into Dawn’s house after the wedding.
At least Mary Anne makes some headway at the Arnold house on her next sitting job. Marilyn and Carolyn are fighting because they each wanted to have friends over to play in their room – but they didn’t want to play together, and they share a room. Mary Anne is finally like, “duh – why don’t you guys move into separate bedrooms?” The twins are on board. When Mrs. Arnold comes home they get her permission and get super excited. When Stacey sits for them a few weeks later, the girls are getting along great and Carolyn even invites Marilyn to join her club with Haley, Vanessa, and Charlotte.
As the wedding approaches, Mary Anne has reconciled herself to the fact that she’ll be moving into Dawn’s house, and she and Dawn have even decided to share Dawn’s bedroom instead of having Mary Anne move into the guest room. They picture themselves doing their homework side by side, sharing all their clothes, and staying up late talking. It’s a nice thought…
Wedding day finally rolls around and it’s bittersweet for Mary Anne. On the one hand, she’s excited, but on the other hand, she’s not a huge fan of change and this is all going to be a big change. The book ends with Dawn and Mary Anne both diving for the bouquet at the wedding reception with an ominous “To be continued in Book #31…”