Cass has a rule about dating summer girls-just say no. Every year, her idyllic beach town is flooded with summer girls, the obnoxious daughters of the rich, who stay in their families' summer homes, sail their yachts, and generally make things unbearable for townies like Cass.

Birdie is the ultimate summer girl. She's the daughter of a wealthy real estate developer dad and a social media influencer mom, and this summer Birdie happens to be in big trouble for accidentally crashing her boyfriend's very expensive car.

Birdie's punishment is to spend the summer with her father at the beach-but it won't be a vacation. He's enlisted the help of Cass, whose dad works for him, to keep Birdie on the straight and narrow, including getting her a job at the public beach where Cass lifeguards.

At first the two despise each other. Birdie doesn't want a babysitter, and Cass doesn't want to be one. But as the season heats up, Birdie surprises Cass time and again, and before long both girls can't help but wonder: Are some rules made to be broken?