Eliza Winters' life runs on spreadsheets. From her color-coded bookshelves to her five-year plan, every detail is meticulously organized. So when her fiancé dumps her for his childhood sweetheart, Eliza's perfectly curated world implodes. The logical solution? Accept a quiet librarian job in the charming coastal town of Harbor Cove, Massachusetts, and rebuild her life according to a new, even more precise, set of rules.

But her new plan has a variable she never accounted for: her new roommate is Jasper Moore, a laid-back marine biologist with perpetually windblown hair, a chaotic approach to life, and a very recent ex-girlfriend—the same woman who is now engaged to Eliza's former fiancé.

To save face in a town where everyone knows everyone's business, the two spurned exes make a pact: they'll pretend to be a couple. The plan is simple, the boundaries are clear, and the arrangement is temporary. But as their fake dates start to feel surprisingly real, Eliza finds her carefully constructed defenses beginning to crumble. Jasper, with his passion for tide pools and his ability to see the woman behind the spreadsheets, is a statistical improbability—a beautiful, chaotic variable that threatens to upend her entire life's equation.

Now, Eliza must make a choice: retreat to the safety of her plans or risk everything on the one factor she never saw coming.