Chapter 3

"What are you studying?" The next morning, Li Chi arrived at the office and found Sun Yuan already engrossed in something on his computer. It looked like some kind of import-export documents? Li Chi noticed an array of beverage bottles scattered across Sun Yuan's desk, overflowing into the trash bin. Does this kid never drink water?

"I'm analysing the city's liquid helium flow data," Sun Yuan continued typing without turning around. "I reconsidered and realized we can't rule out the possibility that he obtained a large amount of liquid helium through some channel to cool the chips. Liquid helium is a rare material, and its movement is relatively easy to trace."

"Any findings?" Li Chi pulled up a chair and sat behind him.

"This is the visualized data of the city's liquid helium flow." Sun Yuan typed a command, producing a chart. Several light spots on the map lit up, connecting to show the flow patterns.

"There aren't many places that use liquid helium, and it's mostly imported from the U.S. I checked each location, and everything's clear, with no reports of losses."

"Have you considered the possibility that the records were hacked and tampered with? The security systems of these research institutes or university labs are often just average." Li Chi pointed out the obvious concern.

"You're right, let me filter..." Sun Yuan input the conditions to screen out institutions that recently reported network intrusions or suspicious account logins.

"Hey, there are indeed some, and quite a few." Names of several institutions lit up. The Tsinghua University Materials Research Institute, the Chinese Academy of Sciences' Institute of Oceanology, and a few other research institutions had all recently reported cyber intrusions. The criminals' methods were incredibly sophisticated, with some incidents leaving almost no trace, merely remote logins from certain users at the most improbable times and places.

"Shall we pay them a visit?" Sun Yuan turned his head to ask.

"Sigh, this case really doesn't allow any rest." Li Chi sighed, but still stood up.

"By the way, Captain Li, I brought you two cryptography textbooks. You can read them on the way; it counts as part of the case."

"...Huh? Fine, I guess." Li Chi groaned. This case had already driven him to the brink of exhaustion, and now he had to study?

"The storage status of the liquid helium?" The warehouse keeper at the Institute of Oceanology entered a query command into the computer, "It's all normal, all the in and out records are accounted for."

"We need to see the actual storage, not just the digital records. We suspect the digital records might have been tampered with." The warehouse keeper was about to say something but clammed up under Li Chi's sharp gaze.

"Follow me." Li Chi and Sun Yuan followed the warehouse keeper through a door and down a staircase. The basement grew colder as they descended, the lighting not quite adequate. The warehouse keeper walked ahead in silence, leading them to a room and casually opening the door.

"This is what you're looking for." To Li Chi's surprise, the liquid helium storage at the Institute of Oceanology was far from high-tech or secure—it was merely a converted office used as a storage room, filled with various containers of all sizes. Some were about the size of a filing cabinet, with wheels at the bottom and simple labels on top that read "liquid helium."

"Your storage measures…" Li Chi was momentarily at a loss for words. Sun Yuan walked up to one of the containers and examined the label.

"Liquid helium isn't used much, and no one would steal it," the warehouse keeper shrugged. "Are you done? I have other things to do."

"No, we need to verify the amount of liquid helium in each container," Li Chi said. He motioned to Sun Yuan. Sun Yuan nodded and gestured for the warehouse keeper to follow him. The warehouse keeper sighed and began checking the pressure gauges on each container, confirming the liquid helium levels.

Li Chi paced around the room. It was a university office, unused, with chairs stacked together, desks that hadn't been moved out, and scattered, outdated equipment covered in a layer of dust. The door wasn't even locked; it opened with a simple twist. This place had hardly any security measures. Given a week, he was confident he could move every container out of this room without any difficulty. But doing so would make it hard to hide his tracks, let alone deceive the digital records.

"No, the amount in this container... doesn't match the records." The warehouse keeper stood in front of one container. Sun Yuan leaned in, squinting at the pressure gauge, trying to understand the correlation between the reading and the stored amount.

"When was the last recorded check? How much is missing?" Li Chi asked.

"A week ago. About two-thirds is gone. The last legitimate withdrawal was a week ago, and we updated the records after that," the warehouse keeper replied with a worried expression. "Now I'm in trouble..."

"Do you have surveillance data?" Sun Yuan asked.

"For the past week? That's a lot..." The warehouse keeper tapped on a tablet. "There are four cameras from here to the warehouse entrance. From the last record to now, there's a total of... 648 hours, 52 minutes, and 16 seconds. Do you need all of it?"

"All of it," Li Chi nodded. Just then, a metallic sliding sound came from one of the liquid helium containers, followed by a hissing noise as a white mist spewed out. The fog quickly dissipated, but Li Chi still felt a gust of cold air, lowering the temperature in the storage room.

"Sorry, I accidentally turned the valve…" For some reason, Sun Yuan's voice became extremely high-pitched.

"Hey! Don't mess with it!" The warehouse keeper's voice also went up several octaves. He hurried over to tighten the valve.

"Luckily, not much leaked." He glanced at the pressure gauge.

"Why has my voice become like this?" Sun Yuan still had that shrill tone.

"It's a characteristic of helium; the speed of sound in the gas is higher, which raises the pitch of your voice. Don't worry, it's not dangerous. Sometimes we inhale a little just for fun," the warehouse keeper said.

Sun Yuan cleared his throat, trying out a few words, but his voice remained unchanged.

"Take us to your security chief; we need to check the video footage," Li Chi brought the matter back on track, though his voice also turned sharp. Sun Yuan's face contorted into a strange expression after hearing Li Chi's words, clearly stifling laughter.

"Let's go." Li Chi motioned to Sun Yuan, "I'll deal with you later." He followed the warehouse keeper out of the storage room.

"Yes, Captain."

"Have you spotted any clues?" Li Chi asked, carrying a cup of coffee as he walked over to Sun Yuan's desk. It was now half past eleven at night, and most of the department had already left. If not for Sun Yuan still being there, Li Chi would have long since gone home. He flipped through the cryptography textbooks Sun Yuan had brought, trying to understand them, but progress was slow—it required too much math knowledge to grasp. Back when he was in the Air Force Electronic Warfare Unit, he would have made every effort to understand these concepts, but that time had passed.

"No," Sun Yuan rubbed his face, having been in front of the screen for over twenty hours, with multiple monitors playing the surveillance footage they had collected from the research institutes. Over the past two days, they had visited several places in the city with liquid helium reserves, and three of them had discrepancies between actual storage and records. Li Chi had tasked Sun Yuan with analyzing the surveillance footage from these locations, even though they had facial recognition software and scene analysis tools, it was still a painstaking task.

"Facial recognition has cleared everyone; there were no strangers in and out," Sun Yuan said, "but all three surveillance videos have missing segments, generally ranging from thirty minutes to an hour."

"Oh? Why is that? Could the suspect have hacked into the system and deleted the video of their entry and exit?" Li Chi's expression grew serious.

"Hehe, Captain Li, do you know how many locations have missing footage? Forty-two, and they're all non-continuous. I can only say, what we can think of, he surely thought of too." Sun Yuan snapped his fingers.

"We can't let this investigation go nowhere, right? With 42 missing segments, we can allocate more resources and expand the search to see if we can identify the suspect. It's just a matter of processing power." Li Chi patted Sun Yuan's shoulder, "Good job. Let's go report to the section chief now."

"Wait, Captain Li, I've found something else." Sun Yuan quickly stopped Li Chi, "This, helium tracing." He pulled up an image, a satellite map with some sort of heatmap overlay.

"Oh? This is a thing?" Li Chi was intrigued.

"Yes. When I accidentally opened the valve earlier, I realized we could trace the suspect's movements by tracking the trace amounts of helium in the air."

"Why didn't you mention this earlier?"

"I used to think helium tracing equipment was typically mass spectrometers with a very short range, only suitable for factory leak detection and not useful for us." Sun Yuan displayed another image. Li Chi knew he was entering show-off mode again, so he just nodded, letting him continue.

"But I got fed up with analysing surveillance footage these past few days, so… I reached out to the resources of the Ministry of Land and Resources' satellite. This thing is equipped with long-range optical analysis devices that can identify atmospheric components by tracking molecular weights. With a little tweaking…" Sun Yuan tapped a few keys, "it can help us detect helium leaks in our city."

The data map on the screen began to move. Sun Yuan motioned for Li Chi to lean in closer. The image resembled a flow of gas, represented as a light blue liquid, swirling and spreading like fog. Sun Yuan indicated the direction of the flow, leading to a clear source—within the city's north eastern district.

"Good job, this will narrow down our search significantly. Let's prepare and head there immediately." Li Chi smiled.

After Li Chi and Sun Yuan departed, the office returned to its usual silence. The dim lights reflected off the dark windows, casting long shadows over the desks and chairs. The rhythmic ticking of the clock echoed through the empty space.

Just as the tranquillity set in, the main computer terminal in the corner flickered back to life, its screen lighting up with streams of code. The cursor blinked, waiting for input. The words "Accessing remote data" appeared on the screen, followed by a prompt for a password.

In the quiet of the night, there was a sudden movement in the shadows, as if something had stirred. A faint, barely perceptible figure appeared near the terminal, blending seamlessly with the darkness. It moved towards the screen, almost floating, its presence felt rather than seen.

The figure's hand or what appeared to be a hand reached out and tapped a key. Instantly, the screen filled with data streams, and the terminal began processing information at an accelerated rate. The figure's form seemed to pulsate in sync with the data flow, as though it was drawing energy or feeding off the digital information.

Then, as quickly as it appeared, the figure vanished into the shadows, leaving behind no trace. The terminal's screen dimmed, the data vanished, and the office returned to its former quiet, as if nothing had happened.