Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
The narrator talks (a lot) about Ligeia.
Right from the beginning, you can tell "Ligeia" definitely doesn't follow the "classic" plot arc. The narrator spends the first third of the story telling us all about Ligeia, about her origins and her beauty and her intelligence and, most of all about her intense devotion to the gal. There's lots of description and no action. You can think of it as "Ligeia: An Introduction."
Conflict
Ligeia suddenly becomes ill and dies.
Just before launching into the story of Ligeia's death, the narrator tells us, "How poignant, then, must have been the grief with which, after some years, I beheld my well-grounded expectations take wings to themselves and fly away" (8). With Ligeia's sickness and death, all of the narrator's dreams are, to put it crudely, flushed down the toilet. He's left with no hope and no guidance.
Complication
The narrator moves to England and marries Lady Rowena Trevanion, of Tremaine. Unfortunately, he hates her.
The narrator admits that he has no idea what to do without Ligeia… so it should come as no surprise when he does something regrettable.
Climax
After a prolonged illness, Lady Rowena dies – but the narrator notices some strange stuff happening almost right away.
This isn't a climax, so to speak, but it is the moment when you know things are going to get really intense. Shadows on the carpet, mysterious drops of red liquid, a sudden turn for the worse, and still pages left to go – you know that the story's not just going to end with the death of Rowena.
Suspense
The narrator watches in horror and amazement as Rowena's body comes back to life – and then falls quickly "back to death." His drugged-up state makes everything a little hazy, but we know that each return – and fall – is more intense than the next.
The first time Rowena shows signs of life, we might think to ourselves: "Man, this is weird." The second? "Huh, what's going to happen?" The eighth, ninth, tenth times? "Come on, this is getting ridiculous!" We really, really want to know what's going down.
Denouement
Rowena rises from her bed, but the narrator notices that something's not quite right with her. She seems to be just a little bit…taller.
The whole "rising from the dead" thing is amazing enough, but Poe's got another twist left in him. Sure, he shows us something unbelievable, but there's still something more to be uncovered.
Conclusion
When the narrator steps closer to Rowena, she lets the shroud drop from her face. She's become Ligeia.
Finally, we get the big reveal. Literally. You could call this the climax if you really wanted to, as this is what everything is moving towards. It's the payoff, and a big one at that.