After offering a quote by Joseph Glanvill claiming that man only yields to death if his will is not strong enough, the unnamed narrator explains that he does not remember any details about his original acquaintance with Ligeia. Although he remembers her knowledge, her beauty, and her thrilling voice, he does not associate the acquisition of these memories with a specific moment. He believes that he met her in an old city near the Rhine River, but he cannot recall what she said about her family, and he never asked for her last name, despite having married her. Despite not recalling these details, he remembers her very clearly and describes her as tall and slender, to the point of emaciation upon her deathbed. He mentions her majestic demeanor and the lightness of her steps, as well as her strange but exquisite features, pale skin, and black, curly hair.
The narrator recalls Ligeia's brilliant black eyes with particular accuracy, as they give him a sense of rapture that he compares to his emotions when viewing certain stars or watching the ocean. He repeats Glanvill's quote and connects it to Ligeia, whose serene exterior hides a fierce passion that her eyes still express, which both "delighted and appalled" the narrator. He also speaks of Ligeia's learning and skill with languages, which surpassed his own knowledge. Because of her superior intelligence, she helps him understand "the chaotic world of metaphysical studies" during their first years as a married couple.
Although the couple lives happily for some time, Ligeia eventually falls extremely ill. Both Ligeia and her husband firmly try to resist her impending death, and not until the last is her placid appearance outwardly disturbed by her mental turbulence. She pours out her love for her husband, who recognizes her wild longing for life, and she asks him to read her verses from a poem that she recently composed. The poem describes a throng of angels watching a play performed by mimes who are controlled by "vast formless things." After a moment, a blood-red crawling object enters and writhes "with mortal pangs" while eating the mimes, to the distress of the angels. The curtain falls, and the angels confirm that the tragedy is called "Man" and the hero is the Conqueror Worm. Ligeia asks if the conqueror can be avoided, and her last words are a reference to Glanvill's quote, affirming her belief that man only dies because of his weak will.
Distraught, the narrator leaves the ancient city on the Rhine and purchases a gloomy old abbey in a remote area of England. He marries the blonde, blue-eyed Lady Rowena Trevanion of Tremaine, and their bridal chamber is a pentagonal room in one of the towers with a window that is tinted so as to give a ghastly light, a vaulted oak ceiling with Gothic and Druidical designs, furniture of Eastern origin and black granite sarcophagi, and gigantic gold tapestries that give a phantasmagoric effect. Rowena does not love her husband and fears his temper, but he loathes her and does not care. Instead, he indulges in opium and dreams of Ligeia's beauty and love.
In the second month of their marriage, Rowena suddenly falls ill and speaks of hearing noises, which the narrator blames on illusions created by the Gothic atmosphere of the bridal chamber. She recovers briefly before commencing a series of increasingly severe illnesses, and the narrator observes that she is fearful of movements in the chamber. To calm her, he goes to give her some light wine, but to his surprise, he senses the shadow of a shade. Being under the influence of opium, he ignores it and pours a goblet of wine for his wife. As Rowena drinks, he thinks he hears someone moving and sees a few drops of red liquid fall into the goblet. Rowena sees nothing, and he guesses that the opium was simply giving him hallucinations.
Three days later, Rowena dies, and the next day, the narrator sits next to her body in the bridal chamber. He recalls the shadow that he saw before looking at Rowena, but instead of thinking of his second wife, he begins to think only about Ligeia. Around midnight, he is startled by a low sob and begins to intently watch Rowena's body. For a few moments, he sees some color return to her face, and he supposes that Rowena is still alive, but he has no way to immediately call the servants and continues to watch. However, soon the body returns to death, and the narrator resumes daydreaming of Ligeia.
After an hour, the process of semi-revival repeats, and the narrator attempts to help her, but she returns to death, and he returns to thoughts of his first wife. The process occurs several more times, and each time the corpse seems to return more finally to death, until eventually she manages to rise from the bed and walk a few steps towards him. The confused and frightened narrator asks himself if Rowena has revived, but he notices that she has grown taller, and he tears away her funeral shroud to find that her hair is not blonde but black. She opens her eyes, and he realizes that Ligeia - not Rowena - is standing before him.
The Lady Ligeia is the central figure in the story, a woman whose dark but wan features and intense personality perfectly suit the Romantic image of the mysterious Gothic woman. She comes from an old city that lies near the Rhine, a river that flows primarily through Germany, the origin of the Gothic story. As in many of Poe's stories, no details are provided that could give a sense of grounding or reality to the tale. The narrator never mentions his origin, and he cannot recall any of Ligeia's past, cementing her otherworldly status. She loves her husband passionately, but she is the dominant member of their marriage because she is imbued with the intelligence - and especially the willpower - that her husband lacks.
The transformation of Rowena's corpse into the revived body of Ligeia causes the two seemingly opposite females to share a physical identity, although they never inhabit the body simultaneously. Whereas Ligeia is ethereal, dark-haired, and strong-willed, Rowena is a fair-haired English bride with blue eyes, and she is destroyed by the darkness to which she cannot become accustomed. She quickly becomes aware of Ligeia's presence, not only in the narrator's mind but in the shadows and secrets of the bridal chamber. The bridal chamber as described by Poe is a truly Gothic setting, where everything seems foreign and lacks a sense of belonging to the earth, much like Ligeia. Rowena dies because even in death, Ligeia is stronger than most humans are in life, both in the sense of having a supernatural will and in the narrator's mind.
The quote attributed to Joseph Glanvill has never been traced to any of Glanvill's writings and may have been an invention of Poe, but it is nevertheless repeated three times within the story, once at the beginning as the epigraph, once by the narrator, and once by Ligeia on her deathbed. The quote suggests that death is merely a matter of man's will succumbing to the inevitable will of God and leaves open the question of whether or not it is possible to overcome death by force of will. Ligeia is the only character of the three in "Ligeia" that potentially has the will to achieve this feat, and she of all three is the most opposed to the idea of death. Poe gives her the authorship of one of his previously written poems about the Conqueror Worm, where death appears vicious and consumes mimes that are already controlled by unseen forces. Whether or not she has in truth come back from the dead, Ligeia unquestionably dominates the lives of both the narrator and Rowena, so she is the only character that might not have a mysterious force controlling her actions. If so, then she alone is exempt from being a mime in the tragedy called "Man."
An initial reading of "Ligeia" provides the case for a supernatural interpretation of the story in which the dead first wife manages to defeat death and her romantic rival in the same blow. However, because of the narrator's hazy memory, obsession over his dead wife, and opium addiction during most of the latter half of the plot, the reliability of his account comes into question. He admits that he disregarded signs of paranormal activity, reasoning that the opium had simply given him a hallucination, and he may have dreamed the apparent revival of Ligeia from Rowena's body because he longed so badly for his first wife, even upon his second wife's death. Opium and romantic madness may have driven him to insanity and led him to poison Rowena without realizing that he was the culprit and not any imagined shade. Because he does not call for the servants, we have no outside witnesses who would be able to confirm or deny his account.
We can view Ligeia in two different ways in relation to the author. Seen one way, Ligeia could represent Poe's concept of the ideal woman, who is strong, intelligent, and beautiful. Physically, this position is almost certainly true, as Ligeia reflects the popular depiction of a striking woman with one strange but compelling feature and an almost consumptive appearance. At the same time, Ligeia could also in spirit and mental faculties be the manifestation of Poe's ideal self, since an author of the early nineteenth century would not necessarily have viewed such a dominant, powerful woman as reflecting feminine perfection. On the feminine outside, she appears placid and passive, but her masculine soul is intellectual and willful. Poe even gives the authorship of his poem to her, thus creating a parallel between himself and the passionate, creative Ligeia. Poe's celebration of intellect and artistry in the stories of C. Auguste Dupin are as present in Ligeia as his understanding of Romantic beauty.