In this thrilling volume of the action-adventure series for younger readers, the group of pals known as the Border Boys find themselves in hot water when their exploration of the open range leads them to a mysterious underground river. It's not only a wonder of nature—it's also a conduit for illegal activities, as the boys soon discover.
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- Available now
- New audiobook additions
- New kids additions
- New teen additions
- Popular Non-Fiction
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