渺無蹤跡 Not A Trace Of Him
那妖滿心歡喜道：「娘娘珍重。卻才那賊乃是孫悟空。他敗了我先鋒，打殺我小校，變化進來，哄了我們。我們這般搜檢，他卻渺無蹤跡，故此心上不安。」那妖满心欢喜道：「娘娘珍重。却才那贼乃是孙悟空。他败了我先锋，打杀我小校，变化进来，哄了我们。我们这般搜检，他却渺无踪迹，故此心上不安。」
逐句解 Line by line
The fiend, his heart full of delight, said, "Have a care, my lady.
重 is zhòng, weighty — 珍重 is to hold something precious, and as an address it means look after yourself. He is delighted and worried in the same breath.
"That thief just now was none other than Sun Wukong.
Nine characters, and this is the first time in the chapter that the name 孫悟空 is said in full. The fiend says it, to the woman standing next to the man himself. 卻才 is the vernacular just now.
"He beat my vanguard, killed my junior officers, changed his shape to get in here, and made fools of us all.
Four clauses, one defeat each. 校 is xiào, a junior officer, not the reading for checking a text. 哄 is hǒng again — the same character the queen was told to use on him, now describing what has already been done to him.
"We have searched like this and he has vanished without a trace, and that is why my mind is not easy."
The base reading gives this character a level tone; 跡 is jì. This is the second 蹤跡 in the chapter — the first was 不見蹤跡, 998 characters back, describing the same failed search from outside rather than from inside the fiend's head.
The fiend explains Sun Wukong to Sun Wukong. He names him, lists his defeats in order, tells the queen the thief got in by changing shape, and finishes by admitting he is frightened — while the thief who changed shape stands a few feet away wearing a maid.
What makes it work is that he is entirely right. Wukong did beat his vanguard, did kill his officers, did change shape to get in, and is at this moment making a fool of him. The fiend is the best-informed character in the room and it does him no good at all, because the one thing he has not worked out is where to look.
渺無蹤跡 is the phrase to notice. 蹤跡 turned up 998 characters ago, at the end of the search that opened the chapter, and here it comes back in the fiend's own mouth. He has been chasing the same absence since dusk. The reader has known where Wukong was the entire time.