Grace, an only child who was adopted at birth, discovers that she is the middle child in her biological family after she gives up her own child for adoption, and she struggles to find belonging as she tries to bond with her stoic older brother and outspoken younger sister.

Cara's mother is missing and the rest of her family is ignoring the problem or is busy with other things. But when a watery specter begins to haunt the family's Cape Cod home, Cara and her brothers realize their scientist mother may not have been who they thought she was. With the help of Cara's best friend Hayley, the brothers and sisters embark on a quest that will lead them from the Cape's hidden, ancient places to a shipwreck at the bottom of...