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.
- New eBooks - Fiction
- New eBooks - Nonfiction
- Available now
- Most popular
- Top eBook Fiction
- Top eBook Nonfiction
- Top eBook Romance
- Top eBook Thrillers
- Women of Royalty - Historial Fiction
- Teen Reads
- Local History
- Romances
- Chills & Thrills
- See all ebooks collections
- Available now
- New audiobook additions
- New kids additions
- Most popular
- Top Audiobook Fiction
- Top Audiobook Thrillers
- Audiobook Mysteries
- Love is Love: LGBTQ Reads
- PBS Presents: The Great American Read
- Toes in the Sand, eBook in Hand: Beach Reads
- Digging in the Dirt: Gardening Books
- Til Death Do Us Part: Marriage Thrillers
- Military Reads
- See all audiobooks collections