Sisters Liz and Nat enjoy an above-ground backyard pool, inviting nerdy next-door neighbor Dan to join them. Nat is older, gorgeous, and the high school social queen, while Liz is heavy and feels overlooked. Dan, attracted to both sisters, thinks he has no chance with Nat, and soon he's partnered with Liz. Dan and Liz's deep intimacy is encouraged by Dan's single (and swinging) mother and the sisters' father. A simple teen romance explodes into lusty combinations.