THE MAGICIAN’S NEPHEW

 
Backdrop #1: Digory’s Mother is dying of cancer.  Because of “a series of unfortunate events,” Digory has brought an evil queen/witch into the newly created land of Narnia.  The creator/redeemer God-figure, the lion Aslan, confronts Digory and charges him to help repair the damage.
Backdrop #2:  CS Lewis’s own Mother died of cancer when he was very young…
 
…a lump came in [Digory’s] throat and tears in his eyes, and he blurted out: “But please, please—won’t you—can’t you give me something that will cure Mother?”  Up till then he had been looking at the Lion’s great feet and huge claws…now, in his despair, he looked up at its face. …the tawny face was bent down near his own and…great shining tears stood in the Lion’s eyes.
 “My son, my son,” said Aslan.  I know.  Grief is great.  Only you and I in this land know that yet.  …It is my wish to plant in Narnia a tree [the Witch] will not dare to approach…  You must get me the seed from which that tree is to grow.”
 Aslan sends Digory and his friend Polly to a special “Garden of Eden” from which he is to pluck an apple.  When he gets to the Garden, he discovers the Witch—she stole in and took an apple for herself—granting her immortality.  He takes an apple for Aslan and is about to leave when the Witch challenges him.
 “But what about this Mother of yours whom you pretend to love so? …Do you not see, Fool, that one bite of that apple would heal her?  …Your home will be happy again….What has the Lion ever done for you that you should be his slave?”
 Digory resists and returns with Polly to Aslan—
 “I’ve brought you the apple you wanted, sir.”
Digory confesses that he almost took another apple for his Mother.  Aslan replies:
 “Understand, then, that it would have healed her; but not to your joy or hers.  The day would have come when both you and she would have looked back and said it would have been better to die in that illness.”
 And Digory could say nothing, for tears choked him and he gave up all hopes of saving his Mother’s life; but at the same time he knew that the Lion knew what would have happened, and that there might be things more terrible even than losing someone you love by death.
 “That is what would have happened, child, with a stolen apple.  It is not what will happen now.  What I give you now [from the tree that was sowed by the apple Digory brought] will bring joy.  It will not, in your world, give endless life, but it will heal.  Go.  Pluck an apple from the Tree.”
 …[Digory] plucked the apple and put it in his pocket.  Then he came back to Aslan.  “Please," he said, "may we go home now?”  He had forgotten to say “Thank you,” but he meant it, and Aslan understood.
 
Perhaps this will encourage you to read (or re-read) the Chronicles.  Only remember to begin at the beginning, with The Lion, the Witch and the Wardrobe