The books in this section are usually hardcover and in decent shape, though we'll sometimes offer hard-to-find books in lesser condition at a reduced price. Though we often put images of the book with their original dust jackets, the copies here won't always (or even often) have them. If that is important to you, please call ahead or say so in the order comments!
Danny and his friend Joe Pearson discover the entrance to a cave in the woods near their home. Professor Bulfinch has just invented a portable x-ray machine, and he, along with his geologist friend Dr. Tresselt see an opportunity to use the device in the cave. The two adults, along with Danny, Joe, and Irene, enter the cave on an expedition. They make an astonishing discovery, but they encounter a significant problem which prevents them from leaving the cave.
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