The Chronicles of Narnia: The Last Battle - C. S. Lewis
During the Last Days of Narnia, Good King Tirian faces the fiercest challenge to any Narnian King's rule ever. Many Narnians think they have seen the great Aslan, but he doesn't behave the way they had expected. The ugly Ape who guards this false Aslan allows him to be seen for only moments at a time, and says that all Narnians have been commanded by the Lion to work for the cruel Calormenes. Many believe it is the real Aslan, and some aren't so sure; but all are afraid to disobey. Only Tirian and his small band of friends have faith that Aslan would never treat his beloved Narnians in this shameful way. They can only hope that their true hero will once again appear in time to save them all.