Margaret Dashwood lives her life according to plan, and it involves absolutely zero heartbreak, thank you very much. Five years ago, love tore her family apart, and since then, she's kept her own heart as safe as possible. It hasn't been easy, especially since her sister Marianne--the world's biggest romantic--has conveniently forgotten that love burned her so badly she literally almost died. So when their oldest sister Elinor invites Margaret along for a Marianne-free summer cruise, she can't wait to soak up every scheduled moment with sensible Elinor before heading off to college.

But just before they set sail, a newly-single Marianne announces that she's crashing their vacation. Suddenly, Margaret's itineraries are thrown overboard, and the ship's cabin feels even tinier with her sister wailing about her breakup from the bottom bunk. The only solution? Find Marianne a dose of love to tide her over until they reach land.

With help from Elinor, her husband Edward, and Gabe--a distractingly handsome new friend on the crew--Margaret sets out to create a series of elaborate fake dates that will give Marianne the spontaneously curated summer romance of a lifetime. But between a chaotic sister, the growing storm of feelings between Margaret and Gabe, and an actual storm on the horizon, this summer is destined to go off course. Margaret will have to decide what's more important--following the plan, or following her heart.