When Mira Holt's hot surfer boyfriend, Zach Wilson, invites her to spend the weekend with him at an exclusive spa, she jumps at the chance to finally be alone with him. She knows she can't get too serious about Zach – she's a mermaid after all, and he's human – but is it wrong of her to want two days of romance and "land sex" before she breaks things off?

Things go badly right from the start, however, when Zach's parents and siblings crash their weekend getaway. The Wilsons seem to have their own reasons for keeping Zach and Mira apart, and lots of questions about Mira's background. Now twelve hours have passed since Mira's bathed in saltwater and her body is starting to shut down. Meanwhile, Zach's acting like he's about to propose and more than anything, she wants to say yes.

Can she escape the spa with her secret intact? Or is land sex with Zach Wilson forevermore reason enough to put her life on the line?