The Secret at the Seashore was published in 1948 as part of the mystery-revised post-war Bobbsey Twins line. The family rents a cottage on the New Jersey shore for a summer holiday, and the bulk of the book takes place around the beach, the boardwalk, and the small coastal town nearby. The seashore setting allows the series to mix swimming-and-sandcastle daily life with a more focused mystery plot.
The central secret of the title involves an elderly fisherman named Mr. Watts who has been behaving strangely on the beach late at night. Bert and Nan investigate and eventually discover that Mr. Watts is searching for a small chest of family heirlooms his grandfather buried decades earlier as a precaution during a war scare. The recovery of the chest provides the satisfying late-book climax. Flossie and Freddie discover a starfish and refuse to throw it back. A representative late-1940s Bobbsey entry.