I am an adult godfather always looking for good books for my young friends. This is one of my three best finds in years. (The others were The Witch of Blackbird Pond, also by Elizabeth Speare, and A Line In The Sand, the Alamo diary in the Dear America series.)
The story is told in the time of Jesus in a village near where Jesus teaches those who come to hear him. Daniel, a young outcast, is sworn to fight the Romans with the goal of throwing them out of the land altogether. There are many other young men who want to do the same thing, but they need a leader. What they do, how they prepare, their speculation whether the new teacher Jesus may be that leader, and most of all, Daniel's struggles between his oath and what Jesus has said to him, are the story.
This is not a religious book, though its end point is the second great commandment Jesus gave (Matthew 22:39). It is a book about life in the time, the unrest and resistance of many Jews to Roman rule, the confusion of many Jews looking for a military messiah trying to decide if Jesus could be that man. But more than that, it is like any other moral tale of any other time, a story of a man trying to decide what is the right thing for him to do.
It is not simplistic, I'm 57 and I read it entirely, but neither is it difficult reading. I strongly recommend it for anyone from 9 years on.