His suspects towards YooJin weren't light. He wouldn't have sent someone after him out of just an instinct or stuff like that.
He couldn't help but notice how nervous the other was to be there, without any logical reason. Why would someone be scared to be in a safe place, where his wounds were taken care of and where he received everything he needed without even being asked for a payment? Who would be so eager to return where he got just stabbed, with the risk the attacker would finish the job? And even more than that, he noticed how YooJin always avoided the stab matter. It's not like an average person gets stabbed every day, it should be something terrifying and traumatizing. How could he not want to do all that was in his might to make sure the stabber would be caught and couldn't cause harm to him, or others, anymore?
In addition to that, YooJin kept blabbing about his family and how worried they were for sure, but never even asked if he could write to them. — Like, if you really have to pretend, at least do it well, babe!

The fact he quickly found out that YooJin lied on his name, giving a different one to literally every person he interacted with, that he chose to stay in the House of Peac*ck by his own will and that he literally vanished without a word as soon as the exits were opened - and about at the same time as when the rumor about the prostitute started to spread - only reinforced his suspects.
Prostitution is not a theme he ever put much thinking on, before. Normally it wouldn't even bother him much, but the thought that someone (let's say) he himself brought to Shiinden and saved could do such a thing there makes his blood boil.

He brought the information to WuXin right away, when ShiSui and Zhui referred it to him, and also shared all of his doubts and suspicions with him, before they decided to send Min to look for YooJin.
He wants this matter to be solved quickly, since he really wants to take the chance of the kids being away to finally have some time alone with WuXin.

When they are told that there is someone working as a prostitute in Shiinden, he gets pissed off really bad. For some reason, his first suspect, since nobody reveals who the person is, automatically becomes YooJin, especially after realising he left Shiinden without any warning.

After checking WonPil's condition and all the people from the Clan Huo, with Qiren's permission, he leaves Cloud Recesses to return to the battlefield, to join the others again. There was no reason to imprison him there, since he helped them and definitely didn't insult Cloud Recesses. XD

After he leaves, the next day, so that they have the time to try to escape and bounce everywhere because of the barriers, all the people who are there are gathered. Qiren forces them all to wear the white uniform of the disciples of ShengHuo. Since XueBao said they are his nephews, they are also allowed to wear the headband, sign they are considered inner members of the clan.
All the kids, plus TiHao and Joohoney, are forced to attend his lectures as well as the other disciples. No matter that they were held captive and enslaved for two years, they had a whole half day to recover so they must be ready for lectures.

Since there is plenty of new faces, nothing can spare them from a full immersion in the rules of the clan. Since there are thousands and Qiren wants to make sure they learn them very well, there will be many, whole mornings of lectures about rules.

Right now, the first lecture just ended and they were let free, for now, but with plenty of homework.

Eventually he decides to go to take a look at WonPil's state, not really caring about himself at that moment.
It's early morning of the day next to when he got out of the cauldron and he uses the telescope to go there, for the first time in his life.

Upon arriving, he approaches the building with the doors open and sees that WuNing is on the floor, like he collapsed there. LaNi approaches him right away to check on him, but concludes that the other just had a narcolepsy incident.
He wakes WuNing up and it doesn't take long for them to realise that WonPil is gone. Entirely, leaving no track behind.

WonPil doesn't say a word, not even the next morning, the situation doesn't appear to change or improve in any way. LaNi can't help but feel that something is off, but he can't figure out what it could be. With WonPil not taking his cloth off for any reason, it's impossible to understand the situation, for those who don't know how that thing works.

If WonPil isn't of help, they only have two options left: cauldron and finding that strange man of the vision. Could it really be that WonPil is being silent because he is trying to protect him? LaNi doesn't know what to think anymore, but he surely doesn't want to sit and wait without doing anything.
To how he sees it, the best option is both, the man and the cauldron. He also wants to see what WonPil could have said to their enemies, if he said anything to them. Actually, LaNi wants to see everything, from the start to the end, regardless how long it will take.

Therefore, LaNi leaves to the House of Scorpion, with the awareness that he could as well miss for a few days if the item decides to show him everything in one go. It doesn't worry him, right now all that he really wants is to get to the bottom of the case, without further delays. He needs to know if there is the chance of an imminent attack or if WonPil really was sent back with a plan against them.
.
On the other side, they have the matter of the mysterious man to take care of. Whoever that is, he is as involved in the matter as a person could be and nothing suggests he could be someone on their side, considering how things went after the events of the vision.
Thanks to LanJi's drawing skills, they get a portrait of that man accurate enough for SangPil to take his shape, find out what he can.

They gather somewhere and bring the matter up, but almost as soon as SangPil transforms into that person, something strange happens: he loses control of his body for a few moments.
He approaches the others, in the shape of that man, and says these words, to the present ones: "The enemy of my enemy is my friend." He just says that and slightly waves, then SangPil is free. But his shape returns to the original one right away and he is not longer able to transform in that man anymore.
Since it was a brief time, he couldn't find out everything about him, but just the following:
- He is called Xie'e, which means evil in Ancient Dolashin, but he doesn't know what his real name is.
- He doesn't know who he is, what he is, where he come from. He woke up with no memories of his past, at some point.
It's not much, but it is certainly enough to attempt to track him down with the Telescope.

As they search for him through the powerful artefact, it indeed shows his position without efforts.
Xie'e is sat on a green field, in front of a strange little outpost, surrounded by black walls, in Asian style. There is a gate behind him, with light pink symbols, looking like spells, that were damaged by someone as to nullify their powers.
Even from the slight openness, from the outside, there can be seen corpses and blood inside the place.

Someone definitely has to go.