C.S. Lewis (Anthony Hopkins) marries Joy (Debra Winger). For a time, her cancer goes into remission, and they enjoy a honeymoon and a happy marriage. Eventually, her cancer returns and she dies.
Lewis is devastated, and comes to realize that much of what he had written in the past about the necessity of pain and of the need to trust in God was overly pat and simplistic. He had been writing about pain and grief in the abstract, but had almost no first-hand experience with those things in the real world.
Ultimately, he regains his faith in God, and with the help of his brother Warnie, tries to be a good father figure to Joy's son Douglas.
Thanks John L!