Lady Rowena marries the narrator; the narrator implies that she's something of a gold digger.
The narrator comes to hate Rowena, and you get the feeling that she hates him back.
Lady Rowena becomes sick and is laid up in the narrator's bridal chamber.
Rowena complains of strange hallucinations, which the narrator passes off as the effects of the bridal chamber.
After recovering from her initial illness, Rowena gets even sicker. The narrator watches over her in her sick bed.
Soon, Rowena's not the only one seeing things: when Rowena begins to faint, the narrator brings in some wine to revive her. Just before Rowena takes a sip, the narrator watches a few ruby red drops of liquid fall into the cup. He doesn't know if he actually saw that happen, though.
Rowena drinks the wine.
Lady Rowena dies a few days later.
The next day, while watching over her body, the narrator hears a sob coming from Rowena's shrouded body. He finds that life has come back to her.
Life leaves her just as quickly, though. A cycle of resurrection and death begins. Each time Lady Rowena revives, however, her lapse into death is even more intense. It's as if her returns to life, which become more and more extreme, lead her to decay even more quickly.
Early in the morning, after a night of "life and death," Rowena rises from her bed and moves toward the narrator. She seems to have grown taller than before.
Rowena removes her shroud. She has become the Lady Ligeia.