Page Hazeltyne is a young woman, trained as a nurse but currently at loose ends. She is living in a boarding house in San Francisco and longing for adventure when she is offered the job of caring for Mrs. Prendergast, a wealthy, eccentric, elderly woman living in a large, secluded house on the coast south of Half Moon Bay. The house, which has been under construction for decades, has been given the moniker "Mystery House" and, as far as Page is concerned, it certainly lives up to its name. The other residents of the house include: Flora Mockbee, the sulky daughter of Mrs. Prendergast's previous companion, who died mysteriously several months earlier; Rand Harwood, a handsome doctor recently arrived from an extended stay in China who is staying on as Mrs. Prendergast's personal physician; and, Lynn, a gentle young man who is suffering from a mysterious mental illness. Page soon discovers that the famous Prendergast diamond, a fabulous pink stone the size of a pigeon's egg named the “Ked Anna,” is missing. She also discovers that some people are willing to kill to possess it.