Complex sentence: Aslan appears and saves Eustace by blowing him into Narnia; then he explains to Jill that she and Eustace are charged with the quest of finding Prince Rilian, Caspian's son, who disappeared years before.
Split into simpler sentences: Aslan appears and saves Eustace by blowing him into Narnia. Then he explains to Jill that she and Eustace are charged with the quest of finding Caspian's son Prince Rilian who disappeared years before.