The Portrait in the Sand — Carolyn Keene

The Danas' pottery teacher, Miss Warren, asks Jean and Louise to help her find her missing fiancé, F.B.I. agent Richard Henley. The girls and Miss Warren stay with her aunt and uncle, the Pattons, while they work on the mystery. The Pattons fear that Henley has drowned, since his boat has washed up on shore.

The Danas find few clues but wonder if the strange hermit, Ham Gert knows anything about Henley. Gert refuses to talk except to warn the girls away from the cliff and the beach. The girls become suspicious of Gert and wonder about the strange cries they hear coming from the top of the cliff. When the girls investigate, the cliff is deserted.

The mystery proves difficult to solve, especially when Lettie Briggs appears on the scene and thwarts the Danas' investigation. How the Danas discover what happened to Richard Henley and help the government will thrill the reader from start to finish.