Ryn is morbidly fascinated by the ocean, and he constantly thinks of ways he might let it consume his life. But each time, something good, no matter how small, stops him from drowning. He might see past his sadness if he could still...well, see.

Asher lives for the future, counting the days until she turns eighteen, when she'll be old enough to move out of her mother's house and feel some control over how she spends her time. She tries to see the good in everyone, probably for the best since she blocks out what they say about her. Not by choice, but she does it.

When Asher and Ryn meet in a group therapy exercise where they have to exchange letters, it's unclear who saves whose life overnight. And when they make a pact to trade their lives for the remainder of the summer, it's evident that they've both found the person who truly understands them: it's only with Asher that Ryn can be himself—a lonely blind boy who might not be so alone after all. And it's only with Ryn that Asher stops feeling so self-conscious about her deafness that she can forget to count down the days and start living them. They spend their summer trading letters and the brightest days of their lives, but when Asher finds a tear-stained letter from a mysterious writer, it becomes clear that she’ll have to choose between who she cares more about saving.