内容简介：
A secret is revealeda] Timmy and Sarah think that a holiday trip to the house of George, their great-grandfather, will be just another boring family visit. After arriving at his unique home, they realize that there is a lot more to George and his longtime companion, Jack, a Boston terrier. While eavesdropping, the children learn of a secret within the house. After their parents and George retire for the evening, Timmy and Sarah venture into the den where they discover a strange key on the table. With Jackas help, the children learn to work together and solve problems, becoming closer and more caring with each other. Together they will discover what lies within the hearthstone, while learning about friendship and family along the waya]