Psychological Profiling: The Tough Captain's Intern

This is my first attempt at a criminal investigation story, so the logic may be a little unclear. If that's not your thing, proceed with caution!!!

On her first day as an intern, she discovers she's being followed. Then she learns that an unsolved case from ten years ago may be connected to her parents. The city's criminal investigation captain is stern, tough, and perpetually scowling, but his words don't match his feelings. His catchphrase changes from “Intern, stay out of the way” to “Su Nianqing, stay behind me.”