Final answer:
In Lamar Giles' book 'Overturned,' the antagonist is not a singular character but rather the systemic issues and corrupt entities in Las Vegas. As the story unfolds, different characters play the role of the antagonist, with the casino owner standing out as a significant adversarial figure.
Step-by-step explanation:
The antagonist in the book Overturned by Lamar Giles is a complex aspect to pinpoint as there are multiple characters who could be seen as causing conflict or opposition. In a broader sense, the main character Nikki's struggle is against the systemic issues surrounding her father's wrongful imprisonment and the corruption in Las Vegas which includes the dodgy casino industry and the criminal underworld. However, if identifying a single character as the antagonist, it mainly shifts among different characters as the story progresses. The most consistent antagonist figure would be the casino owner and the criminal elements involved in framing her father.