The last and perhaps the most mysterious of The Chronicles tells how a simple-minded donkey called Puzzle and a scheming ape named Shift set in motion the final days of Narnia.
Shift dresses the donkey up in a lion skin and pretends that he is Aslan. He lies to the Narnians, saying that Aslan has sold them all to the Calormenes to work as slaves. The truth is that the ape has sold them himself. He also says the evil god Tash is a friend of Aslan. The Narnians, especially the Talking Animals, are puzzle and frightened, but they cannot believe that they are being deceived.
"Please," said the Lamb, "I can't understand. What have we to do with the Calormenes? We belong to Aslan. They belong to Tash ... They say he has four arms and the head of a vulture. They kill men on his altar. I don't believe there is any such person as Tash. But if there was, how could Aslan be friends with him?"
The Ape jumped up and spat at the Lamb.
"Baby!" he hissed. "Go home to your mother and drink milk. What do you understand of such things? But the others, listen. Tash is only another name for Aslan."
With this the ape begins to make use of the selfishness of the dwarfs, the silliness of the ordinary Narnians, the greed of the Calormenes and, finally, the terrible evil of Tash - and this lets loose a flood of destruction over the land.
The many good and brave Narnians fight fiercely under their leader, King Tirian, but in spite of their courage and determination, the end of Narnia is very close. It is then that the real Aslan summons Eustace and Jill, the children from our world, to defend Narnia at the last and most desperate battle.