On a warm summer night in 1816 at the Swiss lakeside chateau of Lord Byron (Gabriel Byrne), the poet and his guests – Percy Bysshe Shelley (Julian Sands); his fiancée, Mary Wollstonecraft (Natasha Richardson); her half-sister, Claire (Myriam Cyr); and his private doctor John Polidori (Timothy Spall) – spend the evening sharing ghost stories while under the influence of experimental compounds provided by the doctor. As the night goes on, reality and the horrific tales begin to commingle.