{Derek} He shook his head. said a voice behind us.We turned to see Simon step out of the doorway. Derek said. He swore. He picked his way across the roof.
Derek was visibly frustrated, shaking his head in response to something that had either been said or done. Just as this moment unfolded, Simon appeared from behind a doorway, catching both Derek and the narrator's attention. This unexpected entrance added tension to the scene as Derek expressed his annoyance more openly.