星夜請牛 Summoning the Old King
妖王道：「你們認得老大王家麼？」六健將道：「認得。」妖王道：「你與我星夜去請老大王來，說我這裡捉唐僧蒸與他吃，壽延千紀。」六怪領命，一個個廝拖廝扯，徑出門去了。行者嚶的一聲，飛下袋來，跟定那六怪，躲離洞中。妖王道：「你们认得老大王家么？」六健将道：「认得。」妖王道：「你与我星夜去请老大王来，说我这里捉唐僧蒸与他吃，寿延千纪。」六怪领命，一个个厮拖厮扯，径出门去了。行者嘤的一声，飞下袋来，跟定那六怪，躲离洞中。
逐句解 Line by line
The demon king said: ‘Do you know the way to the Old Great King's house?’
老大王, the Old Great King -- and this is the Bull Demon King, Red Boy's father, the sworn elder brother Wukong spent four passages claiming kinship with at the start of the chapter. That claim was rejected as nonsense. It is about to become the most important fact in the story.
The Six Valiant Generals said: ‘We know it.’
Two characters. They know the way.
The demon king said: ‘Go for me by night and invite the Old Great King, and say that I have caught the Tang Monk here to steam for him to eat, that his life may be lengthened a thousand ages.’
The invitation, and it explains the whole plot of the novel in one line. Come and eat the Tang Monk with me: 壽延千紀, and your life will be lengthened a thousand ages. 紀 is a long cycle of years. This is why every demon on the road west wants Tripitaka -- his flesh is held to confer immortality, and he is, from a monster's point of view, a walking elixir. The son is inviting his father to share it, which is filial in a way that only works in this novel.
The six fiends received the command and, tugging and jostling one another, went straight out the gate.
The six go out 廝拖廝扯, tugging and jostling one another -- an unruly scramble rather than a military departure. Their names are grander than they are.
The Pilgrim, with a buzz, flew down from the bag, kept close behind those six fiends, and slipped away out of the cave.
And a fly goes with them. Wukong abandons the rescue he was about to attempt and follows the messengers instead, which is the smarter play by a long way: the errand they are running is the thread that leads out of this chapter.
The chapter's last move sets up everything that follows. Red Boy sends for his father the Bull Demon King, offering him a share of the steamed Tang Monk and a thousand ages of added life.
That invitation reaches back to the chapter's opening. Wukong spent four passages insisting he was the Bull Demon King's sworn brother and therefore the boy's uncle, and was laughed at for it. Nobody believed him and the claim achieved nothing. Now the father is being summoned, the whole clan is coming into the affair, and a fly on the wall has just heard exactly where the messengers are going.
The Great Sage leaves his brother in the bag and follows them out. It looks callous and it is correct: the rescue can wait, and the summons cannot.