Set in a decaying coastal town, the story follows two women, Clara and her teenage daughter Eleanor, who live as mysterious vagabonds. They possess a dark secret: they are centuries-old vampires. Clara, the more pragmatic of the two, works as a prostitute to make ends meet, while Eleanor, more introspective and yearning for human connection, writes their unsettling story on paper before discarding it. Their lives take a dramatic turn when Clara meets a lonely man named Noel, who offers them shelter in his dilapidated guesthouse, Byzantium.

As Eleanor reluctantly starts attending the local college, she befriends a sensitive student named Frank. Conflicted about revealing her true nature but desperate to unburden her soul, Eleanor begins sharing pieces of her past with Frank. Meanwhile, Clara's violent methods to ensure their survival cause increasing tension and danger. The two women's presence in the town attracts unwanted attention from a mysterious group pursuing them, pushing their already fragile existence towards a lethal confrontation.