Shenandoah Valley, here I come"", raced vigorously through Malcolm's thoughts as the train sped to an exciting summer at King Arthur's Caverns, operated for tourists by his Uncle Fred. Equipped with a new miner's hat and a carbide lamp outfit, Malcolm came prepared to explore the wondrous caverns. His craving for adventure is more than satisfied when with his friend Debbie, he discovers a tunnel which leads to a gigantic hidden cave in Hollow Hill, complete with waterfalls and an underground lake! Just as the children grasp the importance of this discovery in increasing a slackening tourist trade, they realize that the cave i within the property line of the competitive Grand Arches Caverns. A crisis intervenes when Jerry, the competitor's son, disappears on a solo exploration. Through Malcolm's and Debble's courageous efforts, Jerry is found in the new cave. Both owners then decide to pool their tours using the new cavern as a central high spot. A maximum of action, each chapter ending on a note of suspense, carries the reader smoothly through to the end. With special appeal for boys and spelunkers.