The Night of the Waxing Moon and the Solitary Shadow

The last day of November arrived, the sky a somber, leaden gray. The air was damp and cold, exhaling white mist with every breath, and even the torches in the castle corridors seemed to flicker more erratically than usual. An invisible anxiety, like low atmospheric pressure, hung over some students – especially those sensitive to astronomy or those who knew all too well about certain cyclical changes.

All day, Snape was more silent than usual, the oppressive aura emanating from him almost capable of freezing solid. Even in Potions class, he merely went through the motions mechanically, responding with indifference to Professor Slughorn's praise. His gaze swept sharply across the Gryffindor table from time to time, lingering particularly on Remus Lupin. Lupin today had an unnaturally sallow complexion, his fingers occasionally trembling uncontrollably, but he strove to maintain a facade of calm, joking with Potter and Black beside him, though his smile seemed somewhat forced.

Through the contract, Lin Yanqing could clearly feel the emotions churning within Snape – a mixture of the desire to confirm, the satisfaction of revenge, and a high degree of vigilance, like a volcano on the verge of eruption, forcibly suppressed beneath a cold exterior. He knew that the moment Snape had been waiting to "observe" was tonight.

After the afternoon classes concluded, Snape did not go to the library, nor did he return to the dungeons' common room. He became like a black ghost, silently melting into the castle's intricate shadows. Lin Yanqing tried to vaguely sense his location through the contract, only managing to ascertain that he was moving towards a secluded corner of the castle – likely in a direction that overlooked the path leading to the Whomping Willow.

At dinnertime, Snape was absent from the Great Hall. Lin Yanqing sat at the Ravenclaw table, his appetite gone. He could feel the extreme focus and icy excitement from the other end of the contract, existing in a state of dormancy. Snape had already begun his move.

"Ding dong! (⊙﹏⊙) Contract target detected to have deviated from normal activity zones and entered high-risk monitoring status! Emergency side quest triggered—[Shadow Watch]!"

Quest Description: A full moon night, fraught with peril! The contract target is undertaking high-risk actions alone. As the System's bonded partner, how can the host stand idly by?

Quest Requirements: Ensure the contract target, Snape, remains safe during his actions on this full moon night, preventing him from suffering irreversible severe harm.

Quest Rewards: Concealment Charm (one-time use, can distort the trajectory of one fatal attack) x1, System Points +100.

Failure Penalty: The contract target will randomly receive either a [A week of bad luck] or [Slight blockage of magic circulation] debuff. (T_T)

Lin Yanqing tightened his grip on his fork. The System's quest confirmed his unease. Snape had indeed gone, and the System judged the endeavor to carry "fatal" risk.

"Cub, can you pinpoint his exact location?" he asked urgently in his mind.

"Mmm... the signal is heavily interfered with by magic, probably due to the ancient enchantment in the Whomping Willow area! (;′д｀)ゞ" The System popped up a magical mirror emoji with an empty signal bar. "I can only determine the general direction, pretty much the same as what you sensed!"

No more waiting. Lin Yanqing left the Great Hall quickly and unobtrusively. He didn't try to follow Snape – that would be too easy to detect and far too dangerous. He chose a more circuitous, perhaps more effective, method.

He strode to the Owlery and sent a short, coded note addressed to "S.S." (Severus Snape), reminding him to check if the "constant humidity enchantment for a certain experimental sample was abnormal." This was a pretext they had discussed before regarding the Thestral tail feather powder, a plausible excuse for contact that wouldn't arouse suspicion from outsiders. He hoped this letter, using the school owls' magical tracking, would temporarily interrupt Snape's actions, or at least make him pause and be wary.

Afterward, he went to the eighth floor and entered the Room of Requirement. Tonight, the room, responding to his needs, had transformed into a monitoring room with a massive magical mirror, like a water mirror, capable of displaying blurry images of specific areas. The mirror was filled with mist, only vaguely showing the castle's exterior and the outline of the Whomping Willow area, making it impossible to discern any figures clearly. But this was enough for him to monitor the area for any major commotion.

Time ticked by, each second feeling exceptionally long. The image in the mirror remained blurry, and the emotions from the contract end remained in a state of high-intensity, dangerous focus. Lin Yanqing could feel Snape approaching some core secret; his curiosity and desire for revenge were being greatly satisfied, but the accompanying risks were growing exponentially.

Meanwhile, on the castle's outskirts, in the shadows near the Whomping Willow.

Snape melted into the night, pressing himself against the cold stone wall, his gaze fixed on the giant, wildly thrashing willow tree in the distance. He saw Potter, Black, and that runt Peter Pettigrew, sneaking closer, and then, using some method, they instantly froze the rampaging Whomping Willow. Immediately after, Lupin, wearing ill-fitting clothes and clearly not himself, followed them and slipped into a hole hidden near the tree's roots.

Just as he suspected! They had a secret passage! Lupin's "condition" was definitely related to where this passage led!

A surge of elation, a mix of "I knew it!" and a cold fury of "Finally caught you red-handed!" washed over Snape. He almost couldn't resist rushing out and exposing them on the spot. But his remaining reason told him it wasn't the time; he needed more concrete evidence, needed to know what lay at the other end of the passage.

He stood like a stone statue, waiting patiently in the cold wind, calculating the time. He wanted to know how long they would take to come out, or what would happen inside.

Just then, a school owl, flapping its wings, accurately found the shadow where he was hiding and dropped a note before him.

Snape frowned and impatiently picked it up. It was Lin Yanqing's handwriting, about the constant humidity enchantment for an experimental sample? At this critical moment?

His first reaction was annoyance, thinking it was disturbing his important "observation." But the next second, he keenly sensed something was wrong. Lin Yanqing knew he was conducting an important "observation"; unless it was something extremely urgent and relevant, he wouldn't contact him this way.

"Constant humidity enchantment abnormal..." he muttered the words, his mind racing. Was it a warning? Had something gone wrong in the lab? Or... was this itself a subtle reminder, a reminder that the environment (his situation) had changed and he needed to be vigilant?

He suddenly looked up, gazing again at the dark, deep hole, the alarm bells in his heart ringing from this unexpected message. His plan to move closer was temporarily shelved. He became more cautious, hiding himself deeper, continuing his surveillance with an even sharper gaze, like the most patient of hunters.

Little did he know, this note, seemingly about an experiment, did serve its purpose. It was like a drop of cold water, briefly waking his mind, clouded by revenge and curiosity, preventing him from rashly stepping into the passage that might lead to the werewolf's den at that moment.

In the Room of Requirement, Lin Yanqing saw that there was no major movement in the water mirror. Although Snape's emotions at the other end remained tense, there were no violent fluctuations of panic or pain, and he breathed a slight sigh of relief. The quest completion notification had not appeared, meaning the crisis was not yet over.

It wasn't until late at night, at the peak of the moon's radiance, that Snape saw Potter and the others supporting an almost collapsed, paper-white Lupin, emerge from the hole and quickly disappear into the night.

He had obtained the "evidence" he wanted. Although he hadn't personally seen what was at the end of the passage, Lupin's appearance and the secret passage itself explained a great deal. He prepared to leave, carrying a cold, satisfied sense of victory.

However, as he turned and moved back along his original path through the castle's shadows, he failed to notice a pair of eyes, filled with malice and amusement, not belonging to the Marauders or Lin Yanqing, watching him – this "lone shadow under the moonlit night" – from behind a window higher up on the castle.

Snape believed his actions that night were seamless, unaware that he had fallen under another, more dangerous gaze.