This section of the book focuses on the mishaps and adventures that the kids go through, including Vix and Caitlin and their crushes on two older boys, Joseph "Bru" Brudegher and his cousin, Von.

As the girls mature, they encounter their first heterosexual experiences (Caitlin with an Italian ski-instructor, then Von, supposedly) and Vix's in-depth and long-term relationship with Bru, which continues into her college years when she attends Harvard on a scholarship from The Somers Foundation.

She makes new friends, most notably Maia, her uptight roommate whose worrisome ways begin to grow on Vix, but they become close.

However, things turn sour when Vix realizes she doesn't know what she wants in life and she and Bru temporarily break up during her Junior year of college.

Vix misses Bru, but moves on and casually dates other people, whilst Caitlin has numerous hetero and homosexual escapades in Europe.

The girls keep in loose contact over the years, each becoming busy with her own life until the fateful day when Caitlin makes that phone call and tells Vix about her upcoming nuptials to Bru.

Vix, meanwhile, reconnects with Abby's son Daniel's friend Gus, whom she spent all those summers with years ago at the vineyard.

The closing thought is Vix's recount of her "summer sister" and the memories they will always share, and wishing that things could have ended differently.

In early 2020, Hulu picked up the rights for a limited scripted series based on Summer Sisters following a bidding war with other TV outlets.