This book follows some siblings on their attempt to find an ancient treasure with a map they found hidden in their vacation house in Cornwall, England. With the help of their mysterious Great-Uncle Merry, they set out to solve the map's riddles and evade those who want the treasure for evil purposes.
Very well-written and full of interesting puzzles, this book will keep you entertained and thinking along with the kids. Beautiful descriptions of the setting and the details of the time period also make for great reading about mid-century Great Britain.
The start of The Dark Is Rising sequence.