The Mysterious Fireplace — Carolyn Keene

Jean and Louise are excited to be spending Christmas vacation at Highfort, a property that Captain Dana's friend Tom Fairweather is in the processing of purchasing. The Danas' trip turns out much more exciting than anticipated, because several other people show up at Highfort claiming ownership to the property including arrogant Mrs. Plimpton and the Danas' school friend Sonya Olavu and her brother Tranley. Mr. Fairweather disappears before his arrival at Highfort, further complicating the situation. The Danas feel loyal to Mr. Fairweather, but he cannot defend his claim to the property.

The situation becomes more grim with the disappearance of Sonya's jeweled star and a mysterious nighttime visitor who wrecks the Christmas tree. The Danas must solve the mystery but are at a loss to know how to begin.