Three Children and a Captain

When two brothers and their sister stumble across a cave in the cliffs of Falmouth, they find a deep pool, manmade steps and a large wooden door. A thrilling adventure is about to begin. As the story unfolds with captures, hidden treasure, car and high-speed motor launch chases, will the children and their mother outwit the villains? Or will the Cornish sea claim the lives of the children and their mother tied up in a tunnel with the tide coming in?