Simplify the following text for a Grade 8 native English-speaking person.
Original: Jill and Eustace return to save Narnia from Shift , an ape , who tricks Puzzle , a donkey , into impersonating the lion Aslan , precipitating a showdown between the Calormenes and King Tirian .
Simplified: Jill and Eustace return to save Narnia from Shift , an ape , who tricks Puzzle , a donkey , into pretending to be the lion , Aslan .