Llanvair Castle in Wales is the scene of a complex and intricate search that leads several British teenagers on a merry chase through ancestral documents, medieval and 17th century history and Welsh folklore. Hugh and Gwyn Pryce, summer guests of Sir Owen, are intrigued by their uncle's efforts to recover an ancient family sword. From documents and history books, the intelligent teenagers discover the implications of the sword in the villainous affairs of one ancestor during the historic witch trials as well as it legendary significance. The fact that some unknown person is also determined to find the sword lends a note of special urgency to the mission. Hugh, Gwyn and David (young manager of the estate) pursue and eliminate the suspects on their lies. Tension and danger increase, climaxed with the dual discovery of sword and thieves on the days of the jamboree when Llanvair is opened to the public. For teenagers similar in temperament to these academic and precise detectives, the plot is extremely engrossing. There is a wealth of clues tucked away in the research material and a puzzle that must be pieced together with care and deliberation. A good mystery for the intellectual sleuth.