The boy that approaches is exactly the sort of person that Book had expected to see more of; young, strong, and probably eager for a fight. Exactly the kind of person who Book fears for most.

"Not here, in their castle, no. But, on this planet? Yes. They have not the power to send us home."

"If you believe their cause is worth taking up with no further convincing needed, then, by all means. But wars break out by inches. And what they will ask of us will grow, in time. There are lines that all of us hold our morals to, and war is precisely the thing that will chip away at those lines, if you don't keep your eyes open." He is speaking, still, not just to the boy, but to any who are listening.