What are the main events leading up to the climax of The Magician's Nephew?
Hmm. How far back do you want the chain of events followed?
Polly and Digory go to Charn.
Digory wakes Jadis.
Jadis goes with them to Earth, causing havoc in London.
Polly and Digory use the rings to take Jadis out of London, and accidentally bring others with them.
Rather than going back to Charn, they go to Narnia, where they are present for Aslan's creation of the world. This introduces evil to Narnia, and Digory must go retrieve the magic fruit to fight it; this leads directly to the climax, in which his mother is healed.
Certainly the Narnia/evil/fruit are directly connected; perhaps the others, too?