Here's why:
* Historical Setting: The novel takes place in 17th-century England, specifically during the time of the English Civil War. This historical context is a core element of the story.
* No Futuristic Technology or Concepts: The story doesn't involve any advanced technology, space travel, or other elements commonly associated with science fiction.
* Real-World Historical Events: The novel explores real historical events and figures like Oliver Cromwell and the Parliamentarians, weaving them into the plot.
The novel's suspense and mystery stem from the characters' attempts to uncover the truth about their identities and the political turmoil surrounding them, not from fantastical or futuristic elements.