Sixteen-year old, Sophie Gerrard has been in love with her close friend, Peter Watson since childhood. She planned to tell him how she felt during their families' yearly vacation to the Caribbean. But when Peter arrives from London with a girlfriend and his cousin Ethan, her plans change.Disgusted by how the vacation has turned out, she agrees to go island hopping with Ethan, to avoid Peter. But even that didn't work out as planned. When their dinghy capsizes, Sophie and Ethan are forced to swim to a cliff of rocks. She never planned to share her innermost secrets with Ethan but, she really thinks this could be her last adventure ever. In the panicked hours it takes for help to arrive, Sophie tells him how much she likes her Sunday through Monday undies, that she kissed her best friend's boyfriend, and how she's never made it past third base.Once saved, Sophie tries to forget about all the things she revealed. After all, it's not like she'll ever see Ethan again, right? But Sophie's mom decides he should stay with them while he does his semester abroad, and by the time Sophie realizes she's falling for him, he's moved on to her arch-enemy. Knowing that Ethan can ruin her junior year with one slip, she becomes obsessed with one thought: Please Don't Tell!