The Disappearing Floor

In the 19th installment of the Hardy Boys series, the brothers investigate a mysterious floor which disappears, leading them on a journey of adventure and intrigue. Frank and Joe Hardy are asked by their detective father to help track down a notorious jewel thief and his accomplices. The investigation leads to the outskirts of their hometown and a guarded mansion on the old Perth estate. Alongside their friend Chet Morton, the brothers uncover the mystery of the mansion heir's sudden death, encountering a disappearing floor, a savage-looking hound, a galloping ghost, and a startling invention by a college professor. The boys must navigate through these strange elements to solve both mysteries.