Greydon is a thirteen-year-old boy who loves the sea and the creatures in it. He volunteers at Marine World and becomes convinced that the dolphins should not be kept in captivity, and devises a plan to help free them.

While surfing he gets a glimpse of an exotic creature that he thinks is a mermaid, and when he tells his friends they act like he’s crazy. His brother tells him to drop the mermaid idea. He withdraws from his brother and friends and continues his search to find what he saw. He encounters the mermaid and realizes her safety depends on her never being discovered, especially by Marine World. He tries to protect her from the fate of the dolphins by keeping her a secret. The secret becomes a wedge between him and his friends and brother.