Mary grabbed Dickie's arm and pointed at the hill in front of them.
"Look!" she gasped. "There's a man up there - he's shouting. Something's wrong.
Suddenly, with a thunderous roar, the hill burst open, and a great wave of brown water surged down towards them...
But as the twins face terror in Harkaway Hollow, David and Peter are heading into even greater danger for they have met the Lone Piners' old enemy, the evil Miss Ballinger. And when David sets out to follow her trail, he fails to return.
