藏主變形 The Princess Hidden, the Sage Transformed
那公主果然依行者之言，往僻靜處躲避。也是他姻緣該盡，故遇著大聖來臨。那猴王把公主藏了，他卻搖身一變，就變做公主一般模樣，回轉洞中，專候那怪。那公主果然依行者之言，往僻静处躲避。也是他姻缘该尽，故遇着大圣来临。那猴王把公主藏了，他却摇身一变，就变做公主一般模样，回转洞中，专候那怪。
逐句解 Line by line
The princess did indeed follow Pilgrim's word, and withdrew to some secluded spot to hide.
僻靜處, pì jìng chù, a quiet, out-of-the-way place; 躲避, duǒ bì, to hide, to keep clear.
It was, besides, that her marriage-bond was fated to end, and so she met with the coming of the Great Sage.
The narrator supplies the cosmic warrant in one aside. 姻緣, yīn yuán, is the karmic bond of a marriage — not a choice but an allotment, a tie contracted before either party was born. 該盡, gāi jìn, due to be exhausted, fated to run out. The marriage is not being broken; its term has simply expired, and Wukong happens to be the instrument.
The Monkey King, having hidden the princess away, then gave his body a shake and changed himself into her very likeness, returned into the cave, and waited there expressly for the fiend.
搖身一變, yáo shēn yí biàn, "one shake of the body and a change" — the standard formula for Wukong's transformations, and still the phrase Chinese uses for anyone who changes their colours abruptly. 一般模樣, yì bān mú yàng, the selfsame appearance. 藏 read cáng, to hide — not the zàng of Tripitaka's name.
The trap is set in two swift strokes: the princess concealed, the Great Sage taking her shape to wait inside the cave. The narrator's aside that her marriage-bond was fated to run out supplies the karmic warrant for what follows, framing the impersonation not as mere trickery but as the working-out of a destiny already ripe.
The shape-shifting is the pivot on which the chapter's central deception turns, and the novel lingers on it only long enough to establish the disguise before hurrying off to the provocation at the Baoxiang court. The economy is deliberate. The reader is let in on the ruse in advance, so that the demon's coming credulity — and the comedy of his being consoled by his own enemy — can be relished in full.