Mr. and Mrs. Langmore were found mysteriously murdered in their mansion one morning. Their daughter Margaret, who was at home at the time of the deaths, is quickly suspected of having committed the crime. However, her fiance Raymond Case will not believe in her guilt and convinces the famous detective Adam Adams to investigate. This book was written by Edward Stratemeyer, head of the Stratemeyer Syndicate, under the pseudonym of Chester K. Steele. (Summary by Carolin)