Kindred by Octavia E. Butler
It's a really important "what if" book about race. What if a modern black woman suddenly found herself transported 150+ years into the past, right into the center of the antebellum South? The book doesn't shy away from portraying the realities of that (nothing is sugar-coated, be prepared for some upsetting scenes). This book is addresses many current issues in a way I think a lot of people wouldn't normally take the time to think about - but need to.