Twelve-year-old Summer loves the ocean. The smell, the immensity, the feeling she gets when she dives beneath the surface. She has lived in Barnes Bluff Bay since she was two years old, when Lindy found her on the beach.

It's been the two of them ever since. But now, ten years later, Summer feels uncertainty about her place with Lindy and starts to wonder about where she came from. One night, Summer goes for a swim and gets caught in a riptide, swallowing mouthfuls of seawater.

And that night, she dreams of a girl. A girl her age living in the same town, but not in the same time. Summer's not persuaded that this girl is real, but something about her feels familiar.