一行四眾 Four Of Us In One Party
太監道：「你師兄往那裡去了？」八戒道：「我們一行四眾，師父去倒換關文，我三眾並行囊、馬匹俱歇在會同館。師兄弄了我，他先回館中去了。」太監道：「校尉不要扯他，我等同到館中，便知端的。」太监道：「你师兄往那里去了？」八戒道：「我们一行四众，师父去倒换关文，我三众并行囊、马匹俱歇在会同馆。师兄弄了我，他先回馆中去了。」太监道：「校尉不要扯他，我等同到馆中，便知端的。」
逐句解 Line by line
The eunuch said, "And where has your elder brother gone?"
那 keeps the reading nà even here, where it is asking a question. 那裡 for 'where' is the standing spoken form and takes that reading throughout the chapter's seventy-five occurrences.
Eight Rules said, "There are four of us in one party. The master has gone to get the rescript endorsed, and we three with the baggage and the horse are lodged at the Hall of Common Assembly.
Both instances of 行 read xíng — 一行 is a party travelling together and 行囊 the bag one travels with. These are the chapter's only two places where a number stands in front of the character, and neither is the háng of a row.
"My brother has played a trick on me and gone back to the hostel ahead."
弄 is the plain word for it: not deceived, not betrayed, but played with. It is the same verb the narrator used when Sha Monk saw what was happening and said nothing.
The eunuch said, "Guardsmen, stop hauling at him. Let us all go to the hostel together and we shall know the truth of it."
的 reads dì in 端的, the older spoken compound for what is actually so. The character's usual weak de would leave the phrase meaning nothing at all.
The eunuch settles it in one sentence, and he settles it in Eight Rules's favour. Stop pulling, go and look — which is both the sensible course and the first courtesy anybody has shown him since he was left at the wall.
便知端的 is the first of the chapter's two uses of that phrase; the other is the storyteller's own closing formula, three characters from the end of the chapter. Here it is put in the mouth of a court eunuch who has no idea whose line he is speaking.