The ""mystery"" hardly exists outside of the title, and the strength of this book, as in the author's Mystery of the Missing Dowry (1965), Mystery on a Minus Tide (1964) and others, is in the very realistic portrayal of a small fishing town in Washington State and its people. Gail Miller had been living in Philadelphia with her aunt, and when she returned to her father and stepmother's home in Siah, Washington, after six years she discovered that the town was almost deserted and the residents despondent. A sandbar had made the fishing difficult for them while a neighboring town became more prosperous, the clams were killed when an oil barge broke up, a gang of teenage boys were destroying much of the property, and the remaining population blamed all their problems on an old superstition about a cannon that had disappeared. Gail's enthusiasm for Siah eventually serves as the catalyst for improving the town, and she is also able to help her family--her stepmother and her misfit stepbrother. An often forgotten section of the country is made vital here in an unusual story for girls.