Before that question could take root, the scalpel in Yan Qing’s hand had already opened Leng Yu’s chest. Her movements were precise and practiced — a few deft strokes and Leng Yu’s heart had been removed.

Once the heart was out, Yan Qing used a syringe to fill the pericardial cavity with water, then placed the weighty organ into a basin of water.

Shi Ting watched from the side throughout, filled with curiosity at Yan Qing’s actions, but he held his tongue and said nothing.

Yan Qing took a scalpel and guided it to the base of the heart, drawing the blade lightly across the pericardium. It gave way. A great rush of blood-tinged bubbles surged out — like someone submerged in water who had just punctured a water-filled balloon — rising rapidly to the surface in a frothy mass.

“Just as I thought.” Yan Qing’s eyes were alight, a curve of excitement lifting the corners of her mouth. “If I’m not mistaken, the causes of death for Fan Dongping and Luo Baomei should be the same as Leng Yu’s.”

“How exactly did they die?” Shi Ting voiced the question that had been on his mind.

“I’ll need to verify further.” Yan Qing removed the blood-stained gloves from her hands, put on a fresh pair, and returned to Leng Yu’s body.

This body — she and E’Yuan had examined it multiple times from every angle, and had come up with nothing.

Now that the cause of death was clear, a light had switched on in her mind, and some of the remaining tangles began to unravel.

Yan Qing pried open the deceased’s arm and secured it in place, then used a straight razor to shave away all the hair from the armpit. As the smooth skin was gradually revealed, a small, unassuming puncture mark came into view among the tiny pores.

Wiped clean with alcohol, the mark became even more distinct.

“There it is.” Yan Qing said with quiet excitement. “Found it.”

“Is that a needle mark?” Shi Ting frowned. “The victim was injected with something?”

But no — the toxicology results had already come in long ago. No trace of any drug or toxic substance had been found in the victim’s body.

“Not a substance,” Yan Qing said, lifting the syringe she had used to fill the cavity with water, her eyes narrowing slightly. “Air.”

“Air?”

“The killer used a syringe to inject a large quantity of air into the victim’s body through the armpit. The air entered the circulatory system, blocked the main pathways of the pulmonary artery, and ultimately caused death.”

In the modern era, this condition has a medical name: air embolism.

Yan Qing continued her explanation. “When more than one hundred milliliters of air enters the human circulatory system at once, it can be fatal. The killer understood this threshold and used this method to kill the victims. To draw a comparison — when we are given an intravenous drip and the first bottle runs out, we must always ensure there is still fluid remaining in the drip tube before switching to the next, precisely to prevent air from entering the bloodstream. As for the killer — to avoid leaving a visible needle mark at the injection site, they chose to insert the needle into the armpit, where hair would conceal it. That was my oversight — I failed to shave away all the hair before examining the area.”

It was the first time Shi Ting had ever encountered this method of killing: death by air.

He was stunned, and at the same time his mind was already working at speed, processing and calculating.

Yan Qing added, “As for exactly how much air it takes to kill a person, there is no documented record in the medical literature of this country.”

She had drawn on the knowledge of the modern era — knowledge that did not yet exist in this time.

“The killer must have had some medical knowledge. Speculating further — in order to determine the precise lethal dose, they may have even conducted experiments.”

Shi Ting’s brow creased. “You mean that before Leng Yu and the others, there may have been other victims?”

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