For Louna, weddings are a science: she can handle out-of-control bridesmaids, nervous brides, and missing ring bearers, and she knows exactly what to do with fresh flowers, fairy lights, and mason jars. Louna's mom, Natalie, is a sought-after wedding planner, and for Natalie (divorced) and her business partner, William (chronically single), romance is a science, too: they're scarily accurate when it comes to betting on how long a marriage will last. Louna, though, believes she's already had her romance-a summer-fling-turned-real that ended tragically. So when no-strings serial dater Ambrose barrels into her life, Louna is immune to his charms. But life, it seems, doesn't always go as planned.