If a book provides me with a good story and also teaches me something, then that is a 5 star rating. Fiction is of course just that; made up, possibly without a shred of reality. However, most of my reading has a historical background and it is that that sends me to delve further.
The last Runaway by Tracy Chevalier led me to learn a lot more about the laws that surrounded the whole issue of slavery, particularly in the late 1800s. And then having read A Gentleman in Moscow by Amor Towles, I had to look into more of the history of the Russian Revolution, the time of Lenin and then Stalin. I really enjoyed the research.