While visiting Devil's Leap, the drought-stricken farm belonging to their mother's old school friend, Archibald Darvil, Robert and Annie learn of the mysterious disappearance of Lord Darvil, the patriarch of the Darvil fortune, who disappeared a hundred years earlier, along with the largest diamond ever found on the farm – the supposedly cursed Renaissance diamond.

Together with their new friends, Ellie and Anton, two dogs named Butter and Peanut and a cat named Rufus, the children embark on an adventure that will not only unearth age-old secrets but also change the landscape of the farm forever.