借屍還魂 A Borrowed Body
那閻王卻檢生死簿子看時，他夫妻們都有登仙之壽，急差鬼使送回。鬼使啟上道：「李翠蓮歸陰日久，屍首無存，魂將何附？」閻王道：「唐御妹李玉英今該促死，你可借他屍首，教他還魂去也。」那鬼使領命，即將劉全夫妻二人還魂，同出陰司而去。那阎王却检生死簿子看时，他夫妻们都有登仙之寿，急差鬼使送回。鬼使启上道：「李翠莲归阴日久，尸首无存，魂将何附？」阎王道：「唐御妹李玉英今该促死，你可借他尸首，教他还魂去也。」那鬼使领命，即将刘全夫妻二人还魂，同出阴司而去。
逐句解 Line by line
When King Yama examined the register of life and death, he found that this husband and wife both had years yet due them for ascending to immortality, and quickly dispatched a demon to send them back.
登仙之壽 is a span of years that leads toward immortality — not merely time left over, but a future the register still has plans for. 差 is chāi, to dispatch.
The demon reported, 'Li Cuilian has dwelt in the shades a long while; her corpse no longer survives — to what shall her soul attach?'
A practical objection from a functionary. 歸陰日久 is "long since gone to the shadow world," and the difficulty is administrative: the body has rotted. 魂將何附 — "what will the soul attach to?" — is the question the plot has been waiting for someone to ask.
King Yama said, 'The Tang emperor's sister, Li Yuying, is due to die untimely this very day — you may borrow her body, and have Cuilian's soul return to life in it.'
And the answer was set up thirty-eight passages ago, when the Kings mentioned in passing that the emperor's sister would not live long. 御妹 is the emperor's younger sister, Lǐ Yùyīng. 促死 is to die before one's time. 借屍還魂, "borrow a corpse to return the soul," is a phrase still in daily use for anything discredited that comes back wearing a new name; 教 is jiào and 還 is huán.
The demon received the command, and at once restored Liu Quan and his wife to life, and together they went out of the shadow-world.
即將…還魂 is "thereupon had them return to life"; 還魂 is huán hún. A husband going back to his own body, a wife going back to somebody else's, and nobody upstairs warned.
The chapter's last device is 借屍還魂, returning to life in a borrowed body.
Li Cuilian's own corpse is long gone, so Yama assigns her the body of the emperor's sister, Lǐ Yùyīng, whose untimely death the Kings had mentioned to Taizong in passing at the tribunal. Two loose threads — the sister's short life and the reunited couple's return — are knotted together here, and the melon errand is set up to end, in the next chapter, in a thoroughly domestic tangle of mistaken identity inside the palace.