Rebecca is a Gothic mystery novel. The Gothic genre was most popular in England in the 18th and 19th centuries and emerged alongside shifting attitudes toward social class, property, and inheritance.
Gothic novels often focus on a girl or maybe a hapless young boy who moves into a castle (hence the term "Gothic," because of the architecture) or large aristocratic house. The house will seem as though it is haunted, and it will be next to impossible for the protagonist to leave it. These novels tend to play with the idea of the supernatural, although there usually turns out to be an ordinary explanation for all of the strange and frightening events the protagonist has encountered. For example, a servant might be secretly causing mischief on behalf of a long-lost heir who is back to claim their property. Gothic novels offer an imaginative space for readers and writers to explore the idea of the nuclear family and the ethical dilemmas around property, inheritance, and the division of wealth. The main character is usually forced to "grow up" by learning how to navigate marriage and the family as a way of acquiring wealth and joining the upper middle class.
Rebecca was published in 1938, well after the heyday of Gothic novels, but it nonetheless bears many of the trademarks. Manderley is an aristocratic estate that is haunted by the memory of its dead former mistress. The narrator's coming-of-age process involves figuring out how to step out of Rebecca's shadow and into the role of an aristocrat's wife. In doing so, she elevates her social status. At the same time, in the background of the main plot is the sense that this way of social climbing is outdated. The world is changing, and both Maxim and the narrator need to understand that the general public has less reverence for the aristocracy than it once did. Even the laws governing the inheritance of estates like Manderley are changing. The fire at the end of the book not only draws the plot to a cathartic conclusion, but also sets Maxim and the narrator on their way as a married couple without an ancient estate.
The book also draws on the conventions of mystery novels such as Agatha Christie's famous Hercule Poirot books and Sir Arthur Conan Doyle's Sherlock Holmes. These books typically center on a single crime or a related string of crimes, and they feature a detective with strong deductive reasoning skills who puts together all the clues into an airtight case against one of the key players. Rebecca does not center on a trained detective, but the narrator does spend the book collecting clues and trying to find out what happened to Rebecca. The last third of the novel especially has the characteristics of a mystery novel, as the narrator takes the reader through criminal justice proceedings and continues to piece together Rebecca's last day. All is not revealed until the final chapter, so that the reader spends the book in the kind of suspense most mystery writers would love to create.