A nearly disastrous car wreck in Germany launches 12-year-old Gabriel Zanadu, Alexander, his 14-year-old brother, and their two dogs, Thunder and Lightning, into a sinister adventure near the famous German castle Neuschwanstein.

Unexplained eavesdropping, death threats, and heart-pumping danger drag Gabe, Alex, and the dogs into the clutches of a little-known foreign terrorist network. After they are kidnapped by the terrorists, the scraped and bruised boys battle their captors in underground caverns for freedom. Remembering lessons from their military dad and home-schooling mom, Gabe and Alex struggle to escape the deadly situation.