I think Coleridge was bad at plot. He claimed he forgot the whole story of “Kubla Khan” when a visitor interrupted him, so he could share only the exotic setting.  But Stevie Smith doubts it:

He was weeping and wailing: I am finished, finished,
I shall never write another word of it,
When along comes the Person from Porlock
And takes the blame for it.

Like “Kubla Khan,” “Christabel” is deliciously atmospheric. By the end of Part II, the eponymous heroine is under the spell of the vampiric Geraldine and seems to be doomed. Unfortunately, Coleridge gives up right there. We can appreciate the fragmentary and deeply ambiguous result–yet I suspect Coleridge would have finished “Christabel” if he had thought of a satisfying ending. So here are three possibilities:

1. Geraldine is not a vampire after all. She really was left barefoot under the oak tree by five warriors on white horses. Christabel learns this when she is off moping in the wood (wondering how ere she has sinned), and the five knights come back and kidnap her. They tie her on their white palfrey and ride as fleet as the wind to Tryermaine, the castle of Lord Roland de Vaux. Finding Christabel barefoot under one of his oak trees, Lord Roland sallies forth to punish her abductors. He meets Christabel’s father, Sir Leoline, on a parallel mission to avenge Geraldine. The two estranged friends reconcile and go questing together with their girls in tow. Seeing them together, the five knights appear. They turn out to be the other guys from the old college jousting team. The whole stunt was just a way of getting Roland and Leoline to be friends again. Everyone has a good laugh and Christabel and Geraldine go out with the two cutest knights.

2. Christabel has had a night of mind-blowing sex with Geraldine. She wants more of that–but not with Geraldine, who is high-maintenance and has eyes like a snake. After a lot of histrionic acting, Christabel tells her father that Geraldine is an evil witch. Sir Roland banishes the young woman just to cut down on the drama in his castle (for he “seldom sleepeth well”). Free of that obligation, Christabel hooks up instead with the bard Bracy’s daughter, Kaylee.

3. Geraldine has made up all the spooky stuff to freak out Christabel: the fainting spell at the threshold, the fake tat across her bosom and half her side, the weird stares. Just as Geraldine plans, Christabel runs away to a nunnery to save her soul. That leaves Geraldine free to seduce Sir Leoline, who has been alone since Christabel’s mom died in childbirth. The old baron is weak in health and soon passes. Geraldine inherits the castle and turns it into the most profitable heritage tourism destination resort between Bratha Head and Wyndermere.