Key to the Treasure — Peggy Parish

Each summer Liza, Bill, and Jed visit their grandparents and hear the story of the sketches hung above the fireplace. The sketches are clues to the location of a hidden treasure, and for more than a century, no one has been able to figure them out. The first clue is missing, but when the children stumble upon the second, they're on their way. Could it be that this summer they'll solve the secret that has puzzled everyone for more than a hundred years?