When George’s friend, Katie Firestone, invites Nancy to Deception Island in the San Juan Islands of the Pacific Northwest for a whale-watching excursion, the sleuth arrives to find Katie’s tour boat heavily vandalized. A threatening note warns Katie to "stop meddling." As Nancy investigates, she learns that the town of Snake Horse Harbor is up in arms over an orphaned female orca whale that recently appeared in the channel and has apparently decided to stay. No one has yet figured out what pod she’s from, and it seems that everyone has a different idea of what should be done about her. But one person seems to stand in the way of everyone's plans: a meddling Katie Firestone! As Nancy begins to question her allies, a simple vandalism case begins to unfold into something more mysterious... and sinister.