Unfortunately, the lawn outside the villa revealed no obvious clues, as it was covered in zoysia tenuifolia. This type of grass flourishes most abundantly in the summer and autumn, with well-developed stolons and strong regenerative capabilities. On such a lawn, footprints wouldn't last long unless deliberately trampled.

Feng Bujue then looked up at the window sills and the exterior walls of the villa, but they too were unmarked. However, he wasn't disappointed in the slightest, because he wasn't in a hurry to find the truth at all…

"While it's still light, I'd like to survey the area around the villa. Would you care to join me?" Feng Bujue asked Schofield, who was inside by the window.

"Oh! Yes, of course." Schofield naturally wouldn't pass up the opportunity to consult a renowned detective. He replied, "Just a moment." Before his voice had faded, he turned away from the window, hurried to the doorway, and exchanged a few words with the officer standing guard. Then he returned to the window and, imitating Feng Bujue, climbed out of it. The detective was careful, taking pains not to touch the smear of blood on the windowsill, lest he contaminate the evidence.

Once outside, Schofield followed Feng Bujue as he circled the villa.

"Mr. Feng, you mentioned… a locked room? What do you mean?" Schofield asked.

"Have you read Edgar Allan Poe's *The Murders in the Rue Morgue*?" Feng Bujue inquired.

"Uh… no," Schofield replied. "I rarely read novels."

"Alright… a locked-room murder is a type of so-called 'impossible crime'," Feng Bujue said, not wanting to get bogged down in a literary discussion. "When you entered the house, did you notice the key in the door?"

"Yes, I did," Schofield replied.

"There are two ways to lock this type of door. The first is… for someone inside to turn the copper-knobbed bolt on the back of the lock counter-clockwise when the door is closed. The second is… for someone outside to turn the key twice in the lock when the door is closed," Feng Bujue explained. "Mrs. Carroll discovered the body because the door was locked, and no one answered when she knocked, so she used her key to open it."

Schofield thought for a moment, then continued, "So… when the body was found, the doors and windows of that room were all locked from the inside."

"Inside a sealed space, there is only the deceased, no one else, yet the manner of death clearly indicates it wasn't suicide," Feng Bujue said. "In such cases, the method used by the killer constitutes a locked-room murder."

Schofield responded, "Oh…" He paused, then asked suspiciously, "Wait a minute, in the case before us… what if the killer also had a key?"

"Before you arrived, I already asked everyone in the hallway a few questions, and of course, I asked about that as well," Feng Bujue replied. "In this mansion, each room has two keys, a frequently used one and a spare.

"All the spare keys are kept together on a ring, which Mr. Henderson, the butler, keeps on his person. I've already seen the ring; it's a closed ring, and the keys on it cannot be removed individually. It looks like something out of a medieval dungeon…

"Since Henderson suddenly fell ill and collapsed, Mr. Colson is currently holding the spare keys."

"And the frequently used keys are all separate," he said, taking a key from his pocket. "This is the frequently used key to my guest room, which I found in a drawer in a desk in the room." He paused, then added, "The rooms that are usually unoccupied are cleaned regularly by the maids, so they are usually unlocked, and the keys are simply left inside."

As Feng Bujue spoke, he had reached the rear of the villa. Turning a corner, he continued, "Since the frequently used key to the guest room where the crime occurred was in Mrs. Carroll's possession, there are three possibilities regarding the killer possessing a key… One, the killer is Henderson, the butler; two, the killer stole the spare keys from the butler, killed the victim, locked the door, and then returned the keys; three, the killer managed to duplicate the frequently used key."

Schofield said, "Hmm… You believe this room is a locked room, so you think these three scenarios are unlikely?"

"Correct," Feng Bujue replied. "First of all, the first scenario, Henderson the butler is the killer." He began to explain each one. "That's almost impossible… because the old man had a heart attack when he saw the body and nearly died. I was close enough to him at the time, and there was a doctor present. If that was an act, then Mr. Henderson deserves an Oscar, and Dr. Powell is in on it too.

"Of course, there's also a more extreme hypothesis—schizophrenia. For example… the murder was committed by another personality of Henderson the butler, while the main personality was completely unaware of it."

"Hmm… I see," Schofield nodded.

"The second scenario is equally unlikely," Feng Bujue continued. "Because the risk and difficulty of such an act are extremely high. Getting caught stealing the key would be bad enough, but if he were caught returning it, the murder would be exposed as well. And from the time the killer stole the key until he secretly returned it, Henderson the butler could discover the spare keys were missing at any moment. That period happens to coincide with the time of the murder. If Henderson told the police about this after the crime, then creating a locked room would be pointless."

Before Schofield could respond, Brother Jue immediately moved on to the next point. "The third scenario is more plausible, but…" He suddenly stopped in front of a tree, looked up at it for a moment, then continued, "...but the Dennis couple only visit the villa a limited number of times each year, and they don't stay in the same guest room each time. Because Mrs. Carroll is quite picky, she chooses different rooms with different orientations in different seasons.

"The killer couldn't have predicted which room they would be staying in this time, so… if it were the third scenario, it would mean… other than the rooms that are occupied year-round, the killer stole all the frequently used keys to the remaining rooms and made copies of them.

"And his, or her, purpose, was to one day kill Dennis and make the room look like a locked room."

"That's indeed a bit far-fetched," Schofield replied.

"It's technically feasible, and the risk isn't too great," Feng Bujue said. "But the actual possibility is very low, and… the motive is currently a mystery." He circled the tree in front of him a few times, then glanced at the second-floor windows of the villa before continuing forward. "In conclusion… let's put aside the possibility of the killer possessing a key and consider what other methods could have been used to create this locked room."

Brother Jue's tone was like a teacher asking a student, but the fifty-year-old detective in front of him didn't seem to mind, and asked reverently, "I presume it has something to do with the bloodstains on the windowsill?"

"Actually, the method is simple; it can be done with a relatively strong piece of string. With a little practice, every room with a window in this house can be 'played' with in this way," Feng Bujue gestured towards the villa. "I've finished examining the outside. Let's go inside, and I'll demonstrate for you."