Here's a breakdown:
* The protagonist, Riley, endures unimaginable hardship: She's kidnapped, held captive, and subjected to fear, violence, and psychological manipulation. She experiences deep isolation and despair.
* Despite the challenges, Riley fights back: She uses her intellect, resourcefulness, and courage to survive. She finds ways to maintain her hope and dignity, refusing to let her captor break her spirit.
* The story highlights the power of human connection: Riley's bond with her fellow captive, and her connection to the outside world through the letters she receives, give her strength and fuel her determination to escape.
While the story addresses other important themes like the impact of trauma, the dangers of captivity, and the importance of family and friendship, the core theme is the strength and resilience of the human spirit. Riley's journey demonstrates that even in the darkest of circumstances, there is always hope and the potential to overcome adversity.