Legends of pirate treasure hidden in the tunnels and caves that run under Belfort Island on the Down East coast of Maine are something Maura Ballard uses to entertain children in the after-school program she runs at the island's library, but practical Maura doesn't believe in them herself. They're a useful tool to teach her young charges how to research and work together.

When she's not at work, Maura enjoys the privacy of her home by remote Rose Beach where much of the year, her most frequent visitor is a distinctive, friendly seal. When Belfort's newest police officer, Stephan Kirkland, and his young daughter Maisy move into her neighbor's house, Maura's life is upended in more ways than one. As she and Stephan fall in love, Maura discovers there are far more secrets on her beloved island than she'd ever believed possible. As they come out into the open, life on Belfort will never be quite the same for anyone in the tight knit community.