The Gatehouse Code. The Maple Ridge Inheritance, #3

When thirteen-year-old Tessa Hartford steps into the abandoned stone gatehouse on the edge of the Hartford Eco-Mansion, she expects dust, crooked shelves, and a perfect place to build a summer clubhouse. She does not expect her six-year-old brother to uncover a diamond buried beneath the floor-one that looks suspiciously like the jewels stolen in a string of Hudson Valley heists. With new staff arriving at the mansion, corrupted security footage, and late-night movements no one can explain, the timing is too strange to ignore.
Tessa forms the Trailblazers of Riverview-her tech-savvy brothers, her cautious but brilliant friend Harper, and Benny, who insists on being the official toad handler. Together, they launch a secret investigation across Crabapple Farm, the Hartford property, and the eerie, abandoned Frayne Victorian where a runaway teen has been hiding in the attic. As the Trailblazers dig deeper, they uncover gaps in the mansion's surveillance system, suspicious midnight visits to the gatehouse, and a pattern of activity that points to someone close-someone who knows exactly where the cameras can't see.
Every clue pulls them further into a mystery involving hidden gems, digital footprints, and a network of secrets stretching from the eco-mansion's glass walls to the forgotten corners of Riverview. But solving the case means staying ahead of adults who might shut them down, thieves who might return for what they lost, and a truth that could change everything the Hartfords believe about their new home.