The Great Divorce is an allegory of a journey from one life to another, from earth to heaven. Lewis patterned it after similar works of literature like Pilgrim's Progress and Paradise Lost. The narrator suddenly finds himself on a bus that is headed for heaven. On the bus and in heaven, the narrator encounters several people who represent types of people, or sinners. Some belong in heaven, some do not. Some are still clinging to things in this life. Gradually, the people on the bus realize they have died and are ghosts. People they knew before come to convince them to repent and enter heaven, but most of them choose to return to "the grey city" (earthly life) for various different lame reasons, mostly because they cannot let go of earthly things.
The narrator is the main character and George Macdonald, his guide, is another important character. It is similar to what Dante does in The Divine Comedy with Virgil as his guide. The minor characters are: "Big Man", Len (a murderer), Jack (a murdered man), "The Apostate Bishop", Ikey (blowler hat), The Traveller, The Shame-Filled Woman, The Grumbler, The Flirt, The Artist, Hilda, Pamela, Reginald, Man with the Lizard, Frank and Sarah.
All of the minor characters are allegorical in that they represent types of characters that cannot or will not repent and let go of the sinful world for the sinless world. There are things on earth, the Grey Town, that still hold them - sometimes sin, sometimes people. They have made idols out of the things of the Grey World, so they cannot give them up. They cannot "divorce" themselves from the sinful world, hence the title, THE GREAT DIVORCE.