Natalie, fascinated, was listening to the secret voice which followed her. It was the police detective and he spoke sharply, incisively, through the gentle movement of her mother’s voice. “How,” he asked pointedly, “Miss Waite, how do you account for the gap in time between your visit to the rose garden and your discovery of the body?” “I can’t tell,” Natalie said back to him in her mind, her lips not moving, her dropped eyes concealing from her family the terror she hid also from the detective. “I refuse to say,” she told him.
I can't tell if the detective is real or if she's interrogating herself from a disassociated perspective in order to psychoanalyze herself. I think because of how she was and is being raised, emotions are not valued. So, she might've created this detective voice in her head in order to change the way she thinks and appease her family. Or is the author jumping forward in time and then back discreetly?
