Frederica, living with her aunt in Harper's Green, met Flora and Lucy Lane, and christened their cottage "The house of the seven magpies". When Frederica returns from boarding school, Crispin St Aubyn, the local landowner, plays a part of increasing importance in her life. Then Gaston Marchant arrives, and drama follows, leading to murder, although the murderer remains unidentified. Travelling to Casker Island with Crispin's sister, Tamarisk, Frederic has to find the answer to the riddle overshadowing her life. Only Crispin can tell her, and from him she learns the secret of "The house of the seven magpies".