C. S. "Jack" Lewis (Sir Anthony Hopkins) is a serious professor of literature at Cambridge University. He also write some famous books for children and young teenagers entitled The Chronicles of Narnia. He is also a renown conference speaker and supports his Christian views strongly. He still shares a house with his brother, also a bachelor.
One day, he receives a letter from a person who seems to know and understand him, the American poet Joy Gresham (Debra Winger). She is travelling around the UK in search of an editor for her poems and her son Doug (Joseph Mazzello) would very much meet him. The meeting happens in an old-fashioned pub. Jack has gone there accompanied by his brother Warnie, (Edward Hardwicke) who is also a Cambridge university professor. First, they greet an English-looking lady (Carol Passmore) and Joy looks incredibly modern and different to all the rest of the parisioners, old, male... when she enters the place and shouts aloud if any of them is C. S. Lewis. They invite her to a visit to their home. There, Doug shows to be vivacious and is especially interested in the penthouse, where there is an old wardrobe, the same which opens the way to the magic land of Narnia into Lewis's first novel. Warnie shows it, they unlatch it, and to Doug's disappointment, there are only common coats and jackets. Doug says he had always known it was going to be a normal wardrobe.
Joy and Doug come back to the USA. Jack goes on living as usual: a predictable boring life in which he only talks to other professors, -whom he has philosophical discussions with- and keeps on giving his lectures. In one of these Joy re-appears. She has just come back to the UK after her divorce with her always-unfaithful husband and wants to settle down in London. They meet again, and Jack introduces her to his fellow professors, so everybody thinks they are having an affair. Joy doesn't let cynic Desmond Arding (Julian Fellowes) -and Arnold Dopliss (Roddy Maude-Roxby)- humilliate her, and replies back, which the professor must accept, as he was left speechless.
Jack starts also noticing the motions of student Peter Whistler (James Frain). He is kind of rebellious in his own way although he is also a bright student. One day, he falls sleep during one of Lewis's lessons. Also, Jack sees him stealing a book from a book shop and visits him in his home to offer him some money. Peter rejects it, as it is not a matter of having the means to buy it or not. Peter will leave his studies soon afterwards, and also it isn't lack of money, it is that he considers it useless to finish his studies and move onto teaching at university. Jack will find Peter some years afterwards. Peter has become a school teacher, the same as his late father, and seems contented with his chosen path of life. This makes Jack even more thoughtful about his life, and he has the temptation of wondering about the futility of it all.
Joy and Doug spend Christmas Day at the Lewis'. Joy wouldn't let Doug phone his father, because she knows he's such a careless father.
Some little time after, Joy is finding it hard to be a published author. She asks Jack to marry her so that she can stay in the UK. Jack agrees, and Warnie watches all these motions surprised, although he doesn't oppose it openly. Jack and Joy get married by a judge in a civil wedding, as they don't intend to live together as husband and wife. Joy can now settle down in London with Doug, although she and Jack become the best of friends.
One day, Jack phones Joy. She stops doing whatever she's doing and steps into the corridor in order to answer the phone. Suddenly, she breaks her leg. This is not an accident, because she didn't fall the stairs, of stumbled down, or anything. It just happens like that. It's so painful for her that she can't even crawl to pick the phone up. When at hospital, Jack and Warnie go to see her. It's cancer, and it's very advanced. It's attacked her bones, and that's why her leg bone broke like glass. She has surgery. While his mother is at hospital, Doug goes to live with the siblings.
This makes Jack ponder about his life once again. He changes his Christian speech a little bit, talking about Joy's pain. He proposes to her, as he has realised he's in love. They have a religious wedding, the only one which Jack believes in. Joy and Doug move to the Lewis' for ever as soon as Joy is discharged. Doctors say that her cancer is very advanced, so that it'll probalby reappear. Meanwhile, Joy stays at her new home, and asks to travel around the UK in her honeymoon. First, she moves in a wheelchair, then she uses clutches. Jack and her have many happy moments.
However, she will fall sick again. Doug watches how she gets worst and worst. She will finally die.
His brother and his fellow professors can't sadly offer Jack any consolation. Doug becomes sadder and lonelier as well, and it's not clear if he really approves of her mother having married a different man to his natural father. Although he's never said clearly that his mother is going to die, he knows that it's going to happen. He and Jack have the opportunity of saying goodbye to Joy before she finally dies at her home, not in hospital.
Doug keeps on living with Jack as his father. The last scene shows Jack walking down the same countryside path he had walked by when Joy was sick but still alive.
Doug and a dog run down a green hill while flying a kite.