Wednesday morning at six o’clock, Zhaxi appeared as usual in the institute’s library. It was the third day of the second phase of learning assigned by Yang Ping, and he was studying a paper on guidelines for treating infectious aneurysms. On the table was an open notebook, with a diagram of aneurysm pathological classification on the left, and the course and withdrawal indicators of antibiotic treatment on the right, densely detailed, like a net being woven.

He had gradually grasped the learning method Yang Ping mentioned, not rote memorization, but framework building. Whenever he read a paper, he would draw a mind map in his notebook, attaching new knowledge points to the existing framework. Clostridium difficile infection is the trunk, infectious aneurysm is the branch, intracranial aneurysm is the larger canopy... inflammation, infection, vascular wall repair mechanisms, host versus pathogen competition... He was learning to discern these roots.

The phone vibrated, he glanced at it, it was a message from Professor Yang: "Come to my office."

Zhaxi closed the notebook and hurriedly jogged. The door to Yang Ping’s office was open, but he was not alone. Sitting on the sofa was a middle-aged man in casual clothes, in his early forties, square-faced, thick eyebrows, sitting upright, clearly not a doctor. Beside him was a young woman, around thirty, with short hair, wearing metal-framed glasses, holding a document bag, looking competent.

"Zhaxi, come in." Yang Ping gestured and then turned to the middle-aged man, "This is my student, Zhaxi, from Tibet, trustworthy."

The middle-aged man stood up, extended his hand: "Hello, my name is Yuan, from the Provincial Public Security Department." His handshake was strong, with rough knuckles.

Zhaxi was momentarily stunned, Public Security Department? He glanced at Yang Ping, who nodded slightly, gesturing for him to sit down.

This middle-aged man was Dr. Yuan from the Provincial Public Security Department, not visiting Yang Ping for the first time, and the young woman beside him was his assistant.

Dr. Yuan didn’t beat around the bush: "Professor Yang, trouble has surfaced again. Thanks to you for the last case. This time, things are more complex. We’ve been pondering a lot and still need your help."

Yang Ping leaned back on the chair, speaking calmly: "Tell me about it."

Dr. Yuan glanced at the young woman beside him, who opened the document bag, took out a stack of documents, and placed them on Yang Ping’s desk.

Dr. Yuan introduced the woman next to him: "Xiao He, please give Professor Yang a detailed report."

Xiao He adjusted her glasses, opened the top file, her voice clear and calm: "Case overview: Deceased male, sixty-two years old, retired professor from Nandu University’s Chemistry Department, living alone. Found dead at home three days ago. No signs of struggle at the scene, doors and windows intact, no evidence of forced entry. The corpse had no visible external injuries, no unusual marks such as pinholes or ligatures on the body surface. Preliminary postmortem examination found no lethal pathological changes; toxicological screening is ongoing, with no common toxins detected yet."

She paused, looking at Yang Ping: "However, the deceased’s posture in death was extremely odd. He died sitting at the desk in the study, hands overlapped on the table, head resting on the arms, like taking a nap. A half-drunk cup of tea was on the desk, a book opened to a certain page. The study’s window was slightly ajar, but the screen was intact. The entire scene was very tidy, with no signs of struggle or movement."

Yang Ping listened, expression unchanged, directly addressing the core issue: "Where are the doubts?"

Xiao He and Dr. Yuan exchanged a glance. Dr. Yuan spoke: "Three doubts. First, the deceased was always in good health, undergoing annual check-ups, with no history of cardiovascular diseases. A sixty-two-year-old man, without chronic illnesses, suddenly dying is inherently suspicious. Second, a week prior to his death, the deceased received a threatening letter. The contents pertained to a research project he was involved in thirty years ago; we are still investigating specific details. Third..." he hesitated, glanced at Xiao He.

Xiao He took over: "Third, the deceased’s pupils. During the preliminary postmortem, we found his pupils extremely constricted, almost pin-sized. This is very rare in normal deaths. Opioid intoxication can cause pupil constriction, but the toxicological screening is negative. Additionally, opioid overdose typically manifests as respiratory depression, pulmonary edema, etc., none of which were present."

Yang Ping’s brow slightly reacted, internally repeating, extremely constricted pupils.

"There’s one more point." Xiao He continued, "The deceased’s fingers, his fingertips showed significant pigmentation, gray-brown, limited area but very symmetrical."

Dr. Yuan continued: "I looked up the literature; this presentation doesn’t have clear diagnostic significance, but it seems abnormal to me, just a sense."

Yang Ping’s gaze fell on the stack of documents. He reached out to flip open the first page, it was a scene photo. The deceased was sprawled over the desk, appearing indeed like napping, peaceful to the point of not seeming dead. The book on the desk was opened, Zhaxi leaned close for a look, it was an English version of Advanced Organic Chemistry.

Yang Ping flipped to the next page, a close-up of the pupils. The pupils were indeed very small, almost just a dot.

He then turned to a close-up of the fingers, the pigmentation at the fingertips was very evident, gray-brown, distributed along the nail edges, all ten fingers, highly symmetrical.

"Where’s the complete crime scene report?" Yang Ping inquired.

Xiao He pulled out a thicker file from the document bag: "It’s all in here, including scene photos, item inventory, door and window inspection records, neighbor visit records."