Trixie Belden is having the summer of her life with her new neighbor - and new best friend - Honey Wheeler. A rich girl who enjoys the finer things in life - such as swimming in the cool lake everyday, and solving intrepid mysteries that even the police can't find clues to. Which is why, when the two pals decide to visit an old gatehouse on Honey's property that is covered with vines, and hidden by bushy trees, the two girls are hoping that they will stumble upon a mysterious secret. One that will have them putting their thinking caps on. Lucky for them, the long-abandoned gatehouse in the woods holds just that. For, when the two girls enter the secret hideaway, they discover a very large, very shiny diamond wedged between the floorboards.
A thick wall of blackness surrounded her on all sides, & Trixie felt as though she couldn't breath. She could only stand there, listening, for someone was coming quietly down the back stairs. now he was crossing the hall. Now he was pushing open the swinging door. The beam of a flashlight cut through the darkness, & Trixie whirled around, stifling a scream....