託夢求救 The Dragon Begs in the Emperor's Dream
這涇河龍王也不回水府，只在空中。等到子時前後，收了雲頭，斂了霧角，徑來皇宮門首。此時唐王正夢出宮門之外，步月花陰。忽然龍王變作人相，上前跪拜，口叫：「陛下，救我，救我。」太宗云：「你是何人？朕當救你。」龍王云：「陛下是真龍，臣是業龍。臣因犯了天條，該陛下賢臣人曹官魏徵處斬，故來拜求，望陛下救我一救。」太宗曰：「既是魏徵處斬，朕可以救你，你放心前去。」龍王歡喜，叩謝而去。这泾河龙王也不回水府，只在空中。等到子时前后，收了云头，敛了雾角，径来皇宫门首。此时唐王正梦出宫门之外，步月花阴。忽然龙王变作人相，上前跪拜，口叫：「陛下，救我，救我。」太宗云：「你是何人？朕当救你。」龙王云：「陛下是真龙，臣是业龙。臣因犯了天条，该陛下贤臣人曹官魏征处斩，故来拜求，望陛下救我一救。」太宗曰：「既是魏征处斩，朕可以救你，你放心前去。」龙王欢喜，叩谢而去。
逐句解 Line by line
This Dragon King of the Jing did not return to his water-court but stayed aloft in the air. Waiting until about the hour of zi, he gathered in his cloud-head, furled his mist-horns, and came straight to the gate of the imperial palace.
子時, the hour of zi, runs from roughly eleven at night to one in the morning — midnight, in other words — and takes 子 as zǐ. 霧角, 'mist-horns,' are the wisps of vapor a dragon travels in; furling them is how he arrives at a palace gate without waking anyone. 了 in 收了 and 斂了 is the completive le.
At that moment the Tang king was dreaming that he had walked out beyond the palace gate and was pacing in the moonlight among the shadows of the flowers.
步月花陰 is walking in the moonlight among the shadows of flowers. The emperor's dream carries him out to precisely the gate where the dragon is waiting; the two worlds do not so much meet as coincide.
Suddenly the Dragon King changed into human form, came forward and knelt, crying out: 'Your Majesty, save me, save me!'
跪拜 is to kneel and bow, and 相 in 人相, 'human form,' is xiàng. A Dragon King on his knees in a flowerbed, begging a mortal: the chapter's hierarchies have started to turn over.
Taizong said: 'Who are you? I shall save you.'
當 in 朕當救你, 'I shall save you,' is dāng, 'ought to, shall.' He gives the promise before he has asked who this is. It is made in a dream, and it will hold him in the waking world.
The Dragon King said: 'Your Majesty is a true dragon; I am a dragon under doom. Because I have broken the law of Heaven, I am to be beheaded by Your Majesty's worthy minister, the Registrar of Human Affairs Wei Zheng. So I have come to beg — I pray Your Majesty save me!'
The appeal turns on the honorifics. 真龍, 'true dragon,' is the emperor himself, the Son of Heaven; 業龍 is a karma-dragon, a creature weighed down by his own deeds and facing sentence for them. One word covers both of them, and the petitioner is quietly inviting the emperor to notice the family resemblance.
Taizong said: 'Since it is Wei Zheng who is to behead you, I can save you. Set your mind at ease and go.'
既是 is 'since it is the case that,' and 放心前去 is 'go with an easy mind.' The emperor's reasoning is sound as far as it goes: a sovereign can surely stop his own minister. The chapter will spend the next several passages complicating that.
The Dragon King, overjoyed, kowtowed his thanks and departed.
叩謝 is to knock the head on the ground in thanks. He leaves believing himself saved, which is the second time in this chapter an assurance of safety has proved worth less than it sounded.
The chapter pivots from the water-world to the throne by way of a dream. The Dragon King, giving his own palace a miss, waits until midnight and comes to the gate of the imperial city just as the sleeping Taizong dreams himself walking out under the moon; and there, on the threshold between the two realms, the doomed creature kneels and begs. The scene is spare and swift: a cry, a question, an explanation, a promise.
The appeal works on the logic of sovereignty — 陛下是真龍，臣是業龍, 'Your Majesty is a true dragon, I am a dragon under doom' — casting the emperor as the supreme dragon whose word must govern even a celestial official like 魏徵. Taizong, moved and confident, promises rescue: since it is his own minister who holds the blade, surely he can stay it. It is a reasonable confidence and a doomed one. The chapter has already shown how a promise of safety can fail, and the emperor is about to learn that a minister's duty in a dream is not so easily overruled.