Which C.S. Lewis book tells how Narnia was created and introduces Digory Kirke and Polly Plummer?

The C.S. Lewis book about Narnia’s creation and the adventures of Digory Kirke and Polly Plummer is The Magician’s Nephew.

Published in 1955, The Magician’s Nephew is the sixth Narnia book in publication order but the first in the series’ internal chronology. The story follows Digory and Polly as they use magical rings created by Digory’s uncle Andrew to travel between worlds. Their journey leads to the birth of Narnia and the appearance of its creator, Aslan.

The novel also introduces Jadis, who later becomes the White Witch encountered in The Lion, the Witch and the Wardrobe. A crucial object, the wardrobe, is connected to the wood of a tree that grows from a seed brought back from Narnia. This provides an origin story for the portal used by Lucy Pevensie in the earlier-published novel.

Reading guides sometimes place this book first because of its chronology. Lewis himself published it after five other Narnia stories, so publication order and story order produce different starting points.