If Only begins with Corinna starting eighth grade and ends with her starting ninth. As it ends, it's the first day of Corinna attending the school where her dad teaches, and she's excited to see Clare and Joci again. Her dad's still sad, but he seems more like himself these days, and they've even been laughing occasionally. He's also (finally) learning to cook, and he might be even better at it than her mom—they've been having some decent dinners that don't come out of a can.
Of course, everything's not all sunshine and fluffy bunnies and tasty, moist chicken. Corinna's paranoid that she and Joci will have another falling out, which would mean losing Joci's mom. She also worries that her dad will start dating again—specifically, that he'll start dating her mom's best friend, Deborah. There's a lot of stuff she's still not ready to deal with, but at least now she thinks she and her dad are going to be okay. Heck, she even thinks she catches her dad smiling. Yay.