The chill of late winter and early spring was particularly intense in the mountains.

As soon as she got out of the car, the cold crept up from her calves, spreading throughout her body within moments. Zhen Ai instinctively wrapped her wool coat tighter and walked briskly—not running—towards the ancient castle in front of her.

After a few steps, she felt something was off and paused to look around.

A heavy snowfall had blanketed the area just days before, transforming the trees into a silvery spectacle, creating a peaceful white landscape. The drive up here showcased snow that rivaled the beauty of rime ice.

The world felt unnaturally quiet, only the howling wind filling the air.

The expanse of white around her made the castle's white brick walls seem even more desolate, while the black windows appeared deep and quiet, like eyes watching her intently from the shadows of the snow.

Who would live in such an eerie place?

Shaking off her unease, Zhen Ai pulled out a business card from her pocket.

The card was simple: a white background with black text, devoid of any embellishments or colors. In the center was printed a handwritten name in classical Spencerian script— 

**S. A. Yan** 

**Yan Su, The Man of Letters**

The snow reflected blinding light off the card, casting a glimmer in her dark eyes.

When she received the card from Owen, she was somewhat surprised. A cryptography expert, logician, behavioral analyst, special consultant for the FBI and CIA, along with countless other titles—all reduced to this simple description.

**The Man of Letters. A scholar? A cryptographer?**

It seemed understated but was, in fact, a bold declaration of arrogance.

Zhen Ai ascended the heavy stone steps and pressed the doorbell. The door was opened by a maid with slightly yellowed skin, who spoke in a perfect Southeast Asian accent:

"Miz, please waida minut, ai'll getcha masder, ai'd ly do say u mai suid yourse, but du no."

Zhen Ai took a moment to decipher her words: "Miss, please wait a moment; I'll fetch the master. You may suit yourself, but better not." Zhen Ai nodded, "Thanks!"

The maid turned to leave.

Zhen Ai frowned slightly. The last sentence sounded too much like the master's tone.

Sure enough, as she turned, she noticed a phrase on the wall to her right in the same font as the card:

**You may suit yourself, but do not!**

The warmth of the indoors contrasted sharply with the cold outside. Ignoring the coat rack by the door, she unfastened her coat and loosened her scarf but did not remove any clothing.

Inside the castle was warm and clean, decorated in a Renaissance style. Numerous windows allowed soft light to flood the space, illuminating the aged masterpieces that adorned the walls—a testament to the passage of time.

Zhen Ai stood in the entrance for a while, glancing at her watch. Ten minutes had passed, and the ancient castle was eerily silent. She weighed the large envelope in her hand and ascended a few stone steps, placing the envelope on a side table in the corridor. Turning to leave, her peripheral vision caught a flash of colored light at the end of the hallway.

Curiosity piqued, she turned and walked toward it.

At the end of the corridor was a world transformed—a cascade of colorful light flowed down from above, enveloping everything in a gentle, shimmering glow.

Before her was a spacious round hall, surrounded by wooden bookshelves that stretched from the ground floor to the ceiling dozens of meters high. The shelves were filled with thousands of books, their various colors resembling candies waiting to be sampled.

On either side of the shelves were spiral staircases, leading to circular walkways every couple of meters, making it easy to access the books.

Zhen Ai had never seen such a grand private library. The ancient scent of books seemed to contain a power washed over by time.

A sense of reverence washed over her as she stood in this temple of knowledge.

Looking up, she saw a large circular stained glass window overhead. Sunlight filtered through, creating vibrant cascades of color.

Zhen Ai took a deep breath and slowly lowered her gaze to the white grand piano positioned in the center of the library. It was curious to have a piano here, hinting at the owner's unique interests...

Suddenly, she halted.

As she took a few steps forward and turned her angle, she saw a young man sitting behind the piano.

He appeared to be about twenty-four, with fair skin and sharp Western features—strikingly beautiful, as if he had stepped out of a classical painting. Dark eyebrows framed his light brown eyes, which focused intently on Zhen Ai before he calmly returned to his music.

That glance was so subtle, it felt like he was assessing something. But then again, she wondered if she was overthinking it and approached to greet him.

As she circled the piano, she realized he wasn't sitting on a bench but in a wheelchair.

He was tall, dressed in light-colored sweater and trousers, and seemed comfortable in his chair, engrossed in what appeared to be music notation.

Zhen Ai felt a pang of regret; such a good-looking young man... 

He might have been lost in thought, oblivious to her presence. After a moment, he reached for a book on the piano, appearing to struggle slightly.

Instinctively, Zhen Ai moved to help push his wheelchair. But as her hand extended, she remembered that such "kindness" might be inappropriate. Her hand hovered awkwardly in the air, caught between desire to assist and social etiquette.

He watched her retract her hand, and after a brief silence, raised his gaze to meet hers, his light-colored eyes devoid of emotion but sharp, still probing.

Zhen Ai felt an odd sensation under his gaze. She broke the silence first: "Hello, I'm here to see Mr. Yan Su."

Before she could switch to English, he replied in perfect Mandarin, "I am he."

Zhen Ai froze.

She had heard rumors about Yan Su before coming here—eccentric, reclusive, without friends, living alone in this mysterious mountain castle. Naturally, she had pictured a hunchbacked old man, with a lantern in hand, creeping through the dark corridors, a ghostly light flickering in the black windows.

Knowing that "Yan Su" sounded like "serious", she assumed he was much older. Seeing this young man, she thought he must be Yan Su's son.

Who would have thought that such a legendary figure would be so young?

"Could you please fetch the white book from the bookshelf behind you?" His voice was low and clear, almost musical. "It's the 13th from the bottom in the row facing you, the 5th from the right."

Zhen Ai walked over and retrieved the book. He took it from her and subtly inhaled, his gaze lingering on her fair, slightly flushed hands. He casually asked, "Didn't you bring gloves?"

Caught off guard by the sudden question, Zhen Ai replied, "No." Looking down, she noticed her skin was red and white from the frequent temperature changes.

The man in the wheelchair took out a handkerchief from his pocket and meticulously wiped the parts of the book she had touched.

Zhen Ai was taken aback.

He met her gaze and, without a hint of embarrassment, explained, "Human hands secrete oils. Depending on one's physiology, it can be saturated fatty acids or unsaturated ones, usually slightly acidic. The book has a protective layer, but oils from hands can damage it if not cleaned…"

Noticing her eyes widen slightly, he abruptly stopped, fell silent for a moment, and said, "Forget I mentioned it."

Zhen Ai couldn't help but laugh.

Yan Su's fair face paled slightly. "What's wrong?"

"Nothing."

She remembered Owen's warning—"Don't initiate a handshake; he'll tell you that hands harbor millions of bacteria, and that women have more varied bacteria than men. To respect each other, avoid physical contact, especially handshakes."

Zhen Ai handed him the large envelope. "Owen sent me. He said you could help. Thank you."

Yan Su accepted the envelope, his fingers grazing it with a sense of tactility, then opened it to reveal a card filled with rows of dense numbers: "98.C111 GV943.49 23.E121 DJK734.01…"

"Is this envelope yours, or was it sent along with the card?" 

"It's mine. The card was directly slipped through the door without an envelope." Seeing him deep in thought, Zhen Ai added, "I found it strange, too, that the card came without one."

"Because the paper can reveal a lot. The card is made of common lightweight paper," he narrowed his eyes slightly, raising the envelope, "but this handmade paper is only available from a workshop in Chinatown."

"Just from the envelope, you can tell all that?" Zhen Ai raised her eyebrows in surprise.

His gaze turned slightly distant as he noted her reaction—it felt a bit forced, a sign of deception in her expression.

He returned his focus, placing the envelope and card on the piano lid, lapsing into silence.

Zhen Ai handed him a few more papers. "Oh, Owen said you wouldn't help someone you don't know, so here's my résumé."

Yan Su glanced through it quickly before placing it on the piano as well, remaining silent.

Zhen Ai found his fluctuating demeanor odd—sometimes talkative, sometimes reticent. Just as she was about to ask, the maid returned to inform Yan Su, "Mr. Owen is here."

Owen, being his English name, entered without announcement.

His Mandarin was fluent but slightly off in tone. With a warm smile, he turned to Zhen Ai, "Ai, how's the conversation going?"

Unexpectedly, Yan Su interrupted, "I have something to discuss with you."

He didn't even acknowledge Zhen Ai.

Owen paused, then offered Zhen Ai an apologetic smile, his expression awkward. Zhen Ai didn't mind, muttering a quick, "Excuse me," as she left.

Once she was out of sight, Owen approached Yan Su and kicked his wheelchair lightly. "Can you quit seeking solace in your wheelchair when things get tough?"

Yan Su raised the music sheet he was holding and then set it down, pinching the card between his fingers. "Your friend isn't the client; she didn't receive this."

Owen halted, fully aware of Yan Su's nature—he only accepted cases from clients who came in person.

Owen frowned. "Are you sure? What if…"

"Why so anxious?" Yan Su turned to him, "I didn't say I'm rejecting it."

Owen's mouth fell open, even more surprised.

A: Yan Su believed Zhen Ai wasn't the client. 

B: Yan Su suspected Zhen Ai was lying. 

Result → He accepted?

"Why?"

Yan Su lifted the piano lid again, his long, pale fingers dancing over the keys, producing a light melody. He spoke leisurely, "Because she's in a witness protection program, and you're responsible for her safety."

Owen's spine stiffened, instinctively pushing Yan Su's hand away and slamming the piano lid shut, staring at him, "She—no," He initially wanted to deny it but realized there was no escaping Yan Su's keen eyes.

Yan Su reopened the piano lid, his demeanor calm as he played softly. His voice was refined and deep, harmonizing with the music in a way that seemed to resonate: 

"She has a past injury on her right hand, has been imprisoned and abused, making her highly alert. She likely has one or both parents who are top experts in a specific field, but they're both dead.

She's been to the Middle East and enjoys watching soccer.

She's undergone professional self-defense training, knows the basics of cryptography, and contrary to her résumé, her actual field is likely biology, leaning towards cellular research or pharmaceuticals. Her expertise might rival that of her parents."

"How long did you spend with her? Ten minutes? Five?" Owen was flabbergasted. "How did you figure it out?"

"It's obvious," Yan Su replied, his eyes steady, reflecting the colorful light that spilled through the stained glass overhead, sparkling like rare glass, pure and clear.

What was so obvious… 

Owen opened his mouth, realizing he had foolishly asked.