Tripitaka said, “Good, good.

卻好 twice over — "good, good." Tripitaka has heard the word "somebody" and is already relieved.

It must be some prince of the reigning line, a senior of the court — has he been sent off to garrison somewhere?”

He guesses wrong, and guesses institutionally: a senior royal posted to a frontier command. 親王侍長 is a prince of the blood serving as a senior officer, 長 read zhǎng; 發付 is to dispatch; 鎮守 is to hold a garrison.

The man said, “It is not so.

A flat no. 不是 takes 不 as bú before a falling tone.

In my own palace I have a crown prince, the heir of my own begetting.”

The answer is much closer to home: his own son. 太子 tài zǐ is the crown prince — 子 here carries its full meaning, son or heir, and is zǐ, not the light zi that ends words like 漢子. 儲君 chǔ jūn, the heir-apparent, is the formal term and appears just this once in the chapter, against forty-six occurrences of 太子 — a reminder of how relentlessly this chapter is about a son. (The sealed note gave chú here; the reading is chǔ, as the ruby has it.)

Tripitaka said, “That crown prince — surely the fiend has demoted him?”

The obvious inference, and wrong again: a usurper would surely demote the heir. 貶 is to demote or banish; 那太子 takes the pointing nà.

The man said, “He has not.

不曾 — "he has not." The impostor is far cleverer than that.

He stays only in the Hall of the Golden Bells and the Tower of Five Phoenixes, now expounding texts with the academicians, now attending upon the Quanzhen adept at court.

What he has done instead is give the boy a magnificent, empty life: lectures with the academicians in the 金鑾殿 (the Hall of Golden Bells, the great audience hall) and ceremonial attendance in the 五鳳樓, the Tower of Five Phoenixes. Kept busy, kept honoured, kept exactly where he can be watched.

For three years now the prince has been forbidden the inner palace, unable to meet with the queen his mother.”

And here is the actual cage. Three years barred from the inner palace, and so three years without seeing his mother. 禁 jìn is to forbid; 相見 is to meet one another; 太子 again takes 子 as zǐ.

Tripitaka said, “And what is the reason for this?”

Tripitaka asks the right question at last: why that particular prohibition? 何故 is "for what cause."

The man said, “This is a stratagem the fiend has laid.

計策 is a scheme or stratagem — the ghost knows perfectly well it was designed, not incidental. 那 is the pointing nà.

He fears only that mother and son, meeting, might in idle talk let out the ins and outs of it, and so the secret escape.

The fiend's single fear, and it is a domestic one: that mother and son, left alone, will chat. 閑中論出長短 — in idle talk the 長短 comes out, the long and short of it, the ins and outs. 長 is cháng here, long, not zhǎng, senior. 母子 takes 子 as zǐ; 相見 is again "meet one another."

And so the two do not meet, and he gets to dwell forever and abide unmoved.”

So he keeps them apart, and the reward he expects is stated in the flattest possible terms: 永住常存, to dwell forever and abide unchanged. 得 is dé, gets to.