Key to the Treasure (Liza, Bill & Jed Mysteries)

Plot

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