The novel chronicles the fall from power of the Caliph Vathek, who renounces Islam and engages with his mother, Carathis, in a series of licentious and deplorable activities designed to gain him supernatural powers. At the end of the novel, instead of attaining these powers, Vathek descends into a hell ruled by the fallen angel Eblis where he is doomed to wander endlessly and speechlessly.
Vathek, the ninth caliph of the Abassides, ascended to the throne at an early age. He is a majestic figure, terrible in anger (one glance of his flashing eye can make "the wretch on whom it was fixed instantly [fall] backwards and sometimes [expire]"), and addicted to the pleasures of the flesh. He is intensely thirsty for knowledge and often invites scholars to converse with him. If he fails to convince the scholar of his points of view, he attempts a bribe; if this does not work, he sends the scholar to prison. To better study astronomy, he builds an observation tower with 11,000 steps.
A hideous stranger arrives in town, claiming to be a merchant from India selling precious goods. Vathek buys glowing swords with letters on them from the merchant, and invites the merchant to dinner. When the merchant does not respond to Vathek's questions, Vathek looks at him with his "evil eye", but this has no effect, so Vathek imprisons him. The next day, he discovers that the merchant has escaped and his prison guards are dead. The people begin to call Vathek crazy. His Greek mother, Carathis, tells him that the merchant was "the one talked about in the prophecy", and Vathek admits that he should have treated the stranger kindly.
Vathek wants to decipher the messages on his new sabres, offers a reward to anyone who can help him, and punishes those who fail. After several scholars fail, one elderly man succeeds: the swords say "We were made where everything is well made; we are the least of the wonders of a place where all is wonderful and deserving, the sight of the first potentate on earth". But the next morning, the message has changed: the sword now says "Woe to the rash mortal who seeks to know that of which he should remain ignorant, and to undertake that which surpasses his power". The old man flees before Vathek can punish him. However, Vathek realises that the writing on the swords really did change.
Vathek then develops an insatiable thirst and often goes to a place near a high mountain to drink from one of four fountains there, kneeling at the edge of the fountain to drink. One day he hears a voice telling him to "not assimilate [him]self to a dog". It was the voice of the merchant who had sold him the swords, a mysterious man whom Vathek calls "Giaour", an Ottoman term used for non-believers. The Giaour cures his thirst with a potion and the two men return to Samarah. Vathek returns to immersing himself in the pleasures of the flesh, and begins to fear that the Giaour, who is now popular at Court, will seduce one of his wives. Vathek makes a fool of himself trying to out-drink the Giaour, and to out-eat him; when he sits upon the throne to administer justice, he does so haphazardly. His prime vizier rescues him from disgrace by whispering that Carathis had read a message in the stars foretelling a great evil to befall Vathek and his vizier Morakanabad; the vizier informs Vathek that Carathis advises him to ask the Giaour about the drugs he used in the potion, lest that be a poison. When Vathek confronts him, the Giaour only laughs, so Vathek gets angry and kicks him. The Giaour is transformed into a ball and Vathek compels everyone in the palace to kick it, even the resistant Carathis and Morakanabad. Then Vathek has the whole town kick the ball-shaped merchant into a remote valley. Vathek stays in the area and eventually hears Giaour's voice telling him that if he will worship the Giaour and the jinns of the earth, and renounce the teachings of Islam, he will bring Vathek to "the palace of the subterrain fire" (22) where Soliman Ben Daoud (King Solomon) controls the talismans that rule over the world.
Vathek agrees, and proceeds with the ritual that the Giaour demands: to sacrifice fifty of the city's children. In return, Vathek will receive a key of great power. Vathek holds a "competition" among the children of the nobles of Samarah, declaring that the winners will receive "endless favors". As the children approach Vathek for the competition, he throws them inside an ebony portal to be sacrificed. Once this is finished, the Giaour makes the portal disappear. The Samaran citizens see Vathek alone and accuse him of having sacrificed their children to the Giaour, and form a mob to kill Vathek. Carathis pleads with Morakanabad to help save Vathek's life; the vizier complies, and calms the crowd.
Vathek wonders when his reward will come, and Carathis says that he must fulfill his end of the pact and sacrifice to the jinn of the earth. Carathis helps him prepare the sacrifice: she and her son climb to the top of the tower and mix oils to create an explosion of light. The people, presuming that the tower is on fire, rush up the stairs to save Vathek from being burnt to death. Instead, Carathis sacrifices them to the jinn. Carathis performs another ritual and learns that for Vathek to claim his reward, he must go to Istakhar.
Vathek goes away with his wives and servants, leaving the city in the care of Morakanabad and Carathis. A week after he leaves, his caravan is attacked by carnivorous animals. The soldiers panic and accidentally set the area on fire; Vathek and his wives must flee. Still, they continue on their way. They reach steep mountains where the Islamic dwarfs dwell. They invite Vathek to rest with them, possibly in the hopes of converting him back to Islam. Vathek sees a message his mother left for him: "Beware of old doctors and their puny messengers of but one cubit high: distrust their pious frauds; and, instead of eating their melons, impale on a spit the bearers of them. Should thou be so fool as to visit them, the portal to the subterranean place will shut in thy face" (53). Vathek becomes angry and claims that he has followed the Giaour's instructions long enough. He stays with the dwarfs, meets their Emir, named Fakreddin, and the Emir's beautiful daughter Nouronihar.
Vathek wants to marry her, but she is already in love with and promised to her effeminate cousin Gulchenrouz. Vathek thinks she should be with a "real" man and arranges for Bababalouk to kidnap Gulchenrouz. The Emir, finding of the attempted seduction, bends his head and asks Vathek to kill him, as he is ashamed to have seen "the prophet's vice-regent violate the laws of hospitality." But Nouronihar prevents Vathek from killing her father, and Gulchenrouz escapes. The Emir and his servants plan to safeguard Nouronihar and Gulchenrouz by drugging them and hiding them in a valley by a lake. The plan succeeds temporarily, but when they awake in the valley, they believe they have died and are in purgatory. Nouronihar, however, grows curious and wants to explore the area. Beyond the valley, she encounters Vathek, who is mourning for her supposed death. Both realise the sham. Vathek then orders Nouronihar to marry him, she abandons Gulchenrouz, and the Emir abandons hope.
Meanwhile, in Samarah, Carathis can discover no news of her son from reading the stars. Vathek's favorite wife, the sultana Dilara, writes to Carathis, informing her that her son has broken the condition of the Giaour's contract, by accepting Fakreddin's hospitality on the way to Istakhar. She asks him to drown Nouronihar, but Vathek refuses, because he intends to make her his queen. Carathis then decides to sacrifice Gulchenrouz, but before she can catch him, Gulchenrouz jumps into the arms of a Genie who protects him. That night, Carathis hears that Motavakel, Vathek's brother, is planning to lead a revolt against Morakanabad. Carathis tells Vathek that he has distinguished himself by breaking the laws of hospitality by "seducing" the emir's daughter after sharing his bread, and that if he can commit one more crime along the way he shall enter Soliman's gates triumphant.
Vathek continues on his journey, reaches Rocnabad, and degrades and humiliates its citizens for his own pleasure.
A Genie asks Mohammed for permission to try to save Vathek from his eternal damnation. He takes the form of a saintly shepherd who plays the flute to make men realise their sins. The shepherd asks Vathek if he is done sinning, warns Vathek about Eblis, ruler of Hell, and asks Vathek to return home, destroy his tower, disown Carathis, and preach Islam. He has until a set moment to decide yes or no. Vathek's pride wins out, and he tells the shepherd that he will continue on his quest for power, and values Nouronihar more than life itself or God's mercy. The moment is past, and the shepherd screams and vanishes. Vathek's servants desert him; Nouronihar becomes immensely prideful.
Finally, Vathek reaches Istakhar, where he finds more swords with writing on them, which says "Thou hast violated the conditions of my parchment, and deserve to be sent back, but in favour to thy companion, and as the meed for what thou hast done to obtain it, Eblis permitted that the portal of this place will receive thee" (108). The Giaour opens the gates with a golden key, and Vathek and Nouronihar step through into a place of gold where Genies of both sexes dance lasciviously. The Giaour leads them to Eblis, who tells them that they may enjoy whatever his empire holds. Vathek asks to be taken to the talismans that govern the world. There, Soliman tells Vathek that he had once been a great king, but was seduced by a Jinn and received the power to make everyone in the world do his bidding. But because of this, Soliman is destined to suffer in hell for a finite but vast period — until the waterfall he is sitting beside, stops. This eventual end to his punishment is due to his piety in the earlier part of his reign. The other inmates must suffer the fire in their hearts for all eternity. Too late, Vathek asks the Giaour to release him, saying he will relinquish all he was offered, but the Giaour refuses. He tells Vathek to enjoy his omnipotence while it lasts, for in a few days he will be tormented.
Vathek and Nouronihar become increasingly discontented with the palace of flames. Vathek orders an ifrit to fetch Carathis from the castle. While the ifrit is bringing Carathis, Vathek meets some people who are, like him, awaiting the execution of their own sentences of eternal suffering. Three relate to Vathek how they got to Eblis' domain.[5] When Carathis arrives, he warns her of what happens to those who enter Eblis' domain, but Carathis takes the talismans of earthly power from Soliman regardless. She gathers the Jinns and tries to overthrow one of the Solimans, but Eblis decrees "It is time." Carathis, Vathek, Nouronihar, and the other denizens of hell lose "the most precious gift granted by heaven – HOPE" (119). They begin to feel eternal remorse for their crimes, their hearts burning with literal, eternal fire.
