Jack Henry, Marjorie, and Rose live a carefree life of sibling rivalry and mischief until it is shattered by a tragic accident. Their grandfather, Papa Rattray, has been killed while on his latest expedition. They are rushed off to their ancient family castle in Scotland to attend the funeral. While on their journey to the castle, their father, Ted, fills their minds with a tale of a lost family treasure - Dragon's Eye - and a mythical dragon that once protected the castle. Arriving, they find the castle as ancient as they had envisioned. Spires, giant doors, stone walls and fantastic rooms greet the children along with a motley crew of servants. Their curiosity pushes them to explore the castle in search of the family treasure. With every turn they make, they discover pieces of a puzzle hiding the treasure. In order to solve this puzzle, they must put aside their sibling contention and work together to find the lost family treasure and the reason behind their grandfather's untimely death.