Criminals are always dangerous, but mentally ill criminals pose a whole new layer of unpredictability for law enforcement agencies. That's where Dr. Ko Lap Yan (Alex Fong), a brilliant psychiatrist, comes in. Specializing in diagnosing mentally ill criminals, Lap Yan and his team of psychiatrists and residents at Yan Wo Hospital have close ties to the Serious Crime Unit at the Hong Kong Police Department and Senior Inspector Chung Kwon Ban (Ben Wong).