The Preface explains the origin of the novel. Shelley spent the summer of 1816 near Geneva, Switzerland, where much of the novel takes place. One rainy night, Shelley and her friends challenged each other to write ghost stories. Frankenstein was the only one of the stories to be completed. The Preface also reveals Shelley's aim in writing the novel: to present a flattering depiction of "domestic affection" and "universal virtue."
The origin of the novel as a ghost story places it squarely within the Gothic genre. The statement that the novel is meant to provide a positive image of "domestic affection" indicates that family will be a major theme.