Both a coming-of-age story and a double mystery, the story follows an 11-year-old girl and her 14-year-old brother as they learn about life's challenges during the summer of 1959 in California, a period that came to be called the Gidget era. Set in the formerly grand Surf and Sand Club Hotel, the story also takes the reader back to an even earlier period, the summer of 1938, and the ballroom dancing that the hotel was famous for.
11-year-old Mary Nell Morgan and her brother Lonnie have only been living in the hotel for a little over a year after their mother found employment as the hotel's bookkeeper. They are completely new to California and its beach scene, having lived most of their lives overseas in Saudi Arabia, where their father works on the oil pipeline. While 14-year-old Lonnie quickly falls in love with surfing and the owner's pretty daughter, Jennifer, Nell explores the hotel's dark passageways and swims alone early every morning in the dark and mysterious basement pool, which she considers her secret place.
When the hotel's handyman tells her the story of a beautiful young actress who disappeared in the pool late one night in 1938, Nell resolves to find out what happened to her. She soon discovers that her mother and their family's close friends not only knew the actress but were dancing with her in the hotel's ballroom the night she vanished. That story is told through alternating flashbacks.
When the hotel owner's daughter, Jennifer Hazelwood, goes missing under weirdly similar circumstances, Harry Roach, the original detective from the 1938 case, now nearing retirement, returns to the hotel to help the local police. Mary Nell eventually helps him to solve both cases.
This story is both a family saga and a double mystery, with perhaps a ghostly touch, but its focus is mainly on the feisty young Mary Nell Morgan and the once grand old hotel itself, which the very real Hermosa Biltmore Hotel inspired, and the author's memories of the many weekends he spent there with his mother and their friends in the late 1950s.