Aubrey meets the mysterious Lord Ruthven at a social event when he comes to London. After briefly getting to know Ruthven, Aubrey agrees to go travelling around Europe with him. Aubrey slowly realizes that Ruthven delights in causing the ruin and degradation of others, and after Ruthven attempts to seduce the daughter of a mutual acquaintance near Rome Aubrey leaves in disgust. Alone, Aubrey travels to Greece where he falls in love with an innkeeper's daughter, Ianthe. She tells him about the legends of the vampire, which are very popular in the area, and Aubrey recognises that Ruthven fits the physical description.
This romance is short-lived: Ianthe is killed, her throat torn open by an attacker who injures Aubrey and leaves behind an unusual dagger. The whole town believes it to be the work of an evil vampire. Aubrey falls ill, but is found and nursed back to health by Ruthven. Although suspicious of the man, Aubrey feels obliged to Ruthven and rejoins him in his travels. The pair are attacked by bandits on the road and Ruthven is mortally wounded. On his deathbed, Ruthven makes Aubrey swear an oath that he will not speak of Ruthven or his death for a year and a day, and once Aubrey agrees, Lord Ruthven dies laughing. Amongst Ruthven's belongings Aubrey discovers a sheath which matches the dagger found by Ianthe's body.
Aubrey returns to London and is amazed when Ruthven appears shortly thereafter, alive and well. Ruthven reminds Aubrey of his oath and although Aubrey wants to warn others of Ruthven's character he feels unable to break his oath. Helpless to protect his sister from Ruthven, Aubrey has a nervous breakdown. Upon recovering, Aubrey learns that Ruthven has inherited an earldom and is engaged to his sister, and they are due to be married on the day that his oath will end. Unable to delay the wedding, Aubrey has a stroke. That night, his oath expired, Aubrey relates the entire story before dying. But it is too late: Ruthven has disappeared, leaving his new wife dead and drained of blood.
