Having recently decided to make Purgatory Falls her home, Brooke dives into helping with the annual Founders' Week events. The mermaid and occasional amateur sleuth is tasked with helping tourists, students, and history enthusiasts collect stamps for a special memento, but she quickly gets swept into a search for a stolen bracelet—which leads to the discovery of a dead body.
Meanwhile, a decades-old hunt for treasure foretold to be discovered during Founders' Week has turned dangerous in a way that hits close to home for Brooke. Treasure hunters attack her best friend Twyla's home, a large tree that is a part of the tree nymph herself. Rather than sit around and hope, Brooke decides to end the frenzy and find the treasure herself so she can keep anyone else from being hurt. But Brooke's own history might be wrapped up in the town's, and searching for the treasure puts her in more danger than ever before.