The Ring of Earth (Young Samurai, Book 4)

JACK FLETCHER IS ON THE RUN
With no sensei to guide him, he has just his wits and his swords against many new and unknown enemies, as he journeys along the treacherous road to the port of Nagasaki and perhaps home...

But the Shogun's samurai are hot on his trail. Barely escaping their clutches, Jack runs headlong into a trap. Kidnapped by ninja and led to their village deep in the mountains, Jack has no means of escape.
The only question is who will kill him first - the ninja or samurai?