He goes back to the Jingshi. It doesn't feel like he can breathe as he packs. The packing is extremely light; a water canteen, his qugin, a bundle of talismans. Wangji silently wishes the house farewell.

And then he rides his sword west.

Meanwhile, Jiang Cheng goes to Xichen. 

"Do you have any idea what's wrong with your brother?" 

"...Why, what happened." 

So Jiang Cheng explains what happened: the letter (which he is still VERY CONCERNED over), Wangji's inexplicable reaction, Wangji's anger over his extremely understandable reaction to his inexplicable reaction, Wangji storming off, also that thing where he stabbed himself in the leg a while back???

Xichen is quiet for a long moment. 

Finally: "My brother began behaving differently the morning of the, uh, library incident. He asked me--the first thing he asked me was where your brother was, which seemed odd but not terribly important at the time but which I now have to wonder if it is somehow related. Then he asked me how to tell if you were dreaming; one of the pieces of advice I gave him was to pinch yourself to see if it hurt. When I asked him about the library incident he said he had to be very sure he wasn't dreaming." 

"...You think he knows something." 

"I don't know what to think. But it seems possible." 

"Fuck. Fine, it's not like I have any better leads." 

He doesn't bother to pack anything and therefore arrives outside soon enough to see Lan Wangji take off and follow him. 

Lan Wangji flies towards Qishan.

He isn't sure where the Wens would keep Wei Ying, if they have him, but Wangji will cut his way through their territory until he finds out. If Wei Ying is a prisoner in Nightless City, surely word would spread. Wen soldiers should know, at the very least.

If Wei Ying isn't a prisoner in Nightless City, Wangji will go to Dust Creek Mountain. That his efforts to take care of Xuanwu might have backfired so catastrophically is horrifying, but a possibility.

If Wei Ying isn't there, Wangji will go to Yiling.

He lands once he is too exhausted to continue or once he catches sight of a Wen Sect outpost, whichever happens first.

Maybe it would have been Wen Sect Outpost if he had been sleeping well! Alas. 

Well, that's infuriating.

Fine. He lands in this random forest. He is tired enough that continuing to move around is painful, but Wangji is very adept at ignoring the demands of his body. He moves around as much as is necessary to collect kindling and start a fire.

Shortly thereafter, Jiang Cheng, who has less endurance in general than Lan Wangji but has been sleeping well, lands. 

Wow, what the fuck. 

He glares, a hand flying to Bichen's hilt, and waits for Jiang Wanyin to explain himself.

"Your brother says the morning you stabbed yourself in the fucking leg you asked where Wei Wuxian was. Do you know anything about what's happened to him?" he demands. 

"No." And he doesn't, and he should, and he hates it.

"Do you have anything to go on. Or did you just fly off in a random direction." 

"You've been acting weird for almost a week and now my brother is missing, don't act like I'm the one who's out of line." 

Jiang Wanyin had been loyal to Wei Ying too, at this age. He and Wangji had worked together to find him the last time Wei Ying went missing. He had been a decent ally, and Wangji would be foolish to drive off any cultivator who could help him save Wei Ying. Two people attacking a fortress will go better than one, even if one of those people is objectively the worst.

It's just. Jiang Wanyin does not deserve the number of words he will have to come up with to actually explain this, which is Many. Wangji is extremely annoyed.

"I lived for eight more years than this. A week ago I woke up here, in the past." He stares into the fire. "This did not happen last time. It's too soon."

"What? That's--" impossible, crazy, but not, honestly, that much crazier than stabbing yourself in the leg in the middle of the LIbrary Pavilion. And it would explain the part where he thought he was dreaming. 

He's not convinced Lan Wangji is right, but he thinks he's probably not lying. 

"What do you mean too soon, are you saying this is supposed to happen at some point?"

"Wei Ying went missing while we were at war with Wen Ruohan. For three months we searched for him. It did not happen like this."

"At war with--fuck. What happened? Was he okay?"

"No."

"Fuck." He rubs his face. "And you--got closer, in those eight years, and that's why you're so upset now when you couldn't stand him when he left, okay. Where was he? How did he disappear? It probably wasn't from his undisturbed room, if it was a war. You're headed to Qishan? You think they have him again? What did you change?"

"You three were in hiding. He vanished while you were away.

Soldiers claimed they threw him into the burial mounds of Yiling. But he lived. Wei Ying never told us what happened. 

I will look for him in Qishan first. Then everywhere else."