Autumn is looking forward to summer vacation. She and her best friend plan on going to all the best ice cream places their stomachs can handle -- and in NYC, the possibilities can't get any sweeter. Linnea is still not over the fact that her dad has found love after her parents' divorce. Luckily, she can take out all her feelings on the tennis courts for a winning summer. But then Autumn and Linnea discover the news: their parents are getting married. Devastated, the two of them come up with an idea: if they can split up their parents, their lives can go back to normal. As Autumn and Linnea secretly try to sabotage everything from date nights to wedding planning, the two of them discover that having a sister is not the worst thing after all ...