The Last Battle C.S. Lewis. 1956 Harper Collins. The land of Narnia falls under the siege of Calormenes thanks to the instigation of an Ape who fools a donkey into playing the part of Aslan. Once again, the children are called from their world to help.
King Tirian and Jewel the Unicorn try to fight off the Carlormenes and the talking animals who think Aslan is punishing them for something bad. It is through King Tirian that the story is told. When he is captured, he is freed by Jill and Eustace. The plotting then begins to recover Jewel and thwart the Carlormenes. But as they fight the invaders, they are forced to face the fact that they may fail.
The characters don’t go through an arc really. They do go from fearful of things to accepting. The story is the big thing here. Lewis completes the Narnia saga with the last battle for Narnia. It is a good tale. I did have an issue with one of the characters not returning but other than that, it is a charming story. I think it has more to do with the Biblical verse that one can only enter heaven with the faith of a child though than excluding her because she does something frivolous.