Christabel goes in the woods to pray to the large Oak tree, where she hears a strange noise. Upon looking behind the tree, she finds Geraldine, who says that she had been abducted from her home by men on horseback. Christabel pities her and takes her home with her.
Her father, Sir Leoline, becomes enchanted with Geraldine, ordering a grand procession to announce her rescue. The poem was never finished, and ends here. According to James Gillman, Coleridge planned to finish the poem in the following manner: 
The bard reaches the castle where Geraldine claimed to have been from, but finds the place a ruin, long deserted. Returning back to the castle of Sir Leoline and Christabel, Geraldine vanishes, transforming herself into an old, vanished lover of Christabel. Christabel finds herself disgusted by the return of her old knight, though she does not know why. Ultimately, however, her father persuades her to marry the man, and she consents against her desires. At the ceremony, however, the true knight reappears with a ring of betrothal she had given him years before, proving himself. The supernatural Geraldine vanishes, a bell tolls, Christabel's mother's voice is heard (as predicted), and the marriage recommences happily with the new knight.
Geraldine is an unusual being. Some interpretations claim she has a sexual attraction to Christabel. Her malign influence is felt as the story progresses and she seems altogether unhuman. The character of Geraldine can also be seen as evil early in the poem with her unusual behavior also of that the behavior of things around her such as the mastiff growling at her, and the strange actions of light,which may refer to her closeness to hell.
The plot has been interpreted in various ways, and has been interpreted both as being focused on lesbianism and on the daemonic (among other ways, such as a recapturing of the Medieval lai).