What is the summary of chapters 20 and 21 in Monkey by Wu Ch'eng-en?

In Chapter 20 of Monkey, the prince hears from his mother that the king hasn't been himself for the past three years. The Prince returns to the priest Tripitaka and enlists Monkey to retrieve his drowned father. Monkey coerces Pigsy into assisting him. Pigsy collects the King from the Dragon. In Chapter 21, Monkey and Pigsy take the resuscitated King back to Crow-cock to displace, capture and punish the imposter king. They discover that the imposter had been sent there three years ago as retribution for a crime committed by the true king.
In Chapter 20, during an emotional reunion, the prince's mother confesses that she has for three years wondered about the nature of her husband (his father, the King) who seemed, three years ago, to have suddenly changed so much. Having Tripitaka's story about an imposter king confirmed, the prince returns to him and requests Monkey's assistance in rescuing the true king from his underwater grave. Monkey--who displays his magical powers for the prince--tricks Pigsy into coming along to help by promising him full possession of treasure "worth more than an army of ten thousand men."
After Monkey provides the prince with plenty of game to fulfill the hunt he earlier told the imposter king he was going on (without game, the king might accuse and imprison him), then, when Monkey and Pigsy arrive at the banana-plant and find the well under a "slab of stone," Pigsy is lowered into the well by Monkey's magically stretched cudgel. After more of Monkey's trickery, Pigsy consents to dive down to find the "treasure," which is really the drowned king. On the other side of a guarded under-water portal, Pigsy talks to the "Dragon King of the Well" in his "Crystal Palace."
Pigsy refuses to carry the king--who has been preserved for three years by the Dragon King through a magical pearl--out of his death chamber (because he won't be paid a fee), but the Dragon ejects the king's body along with Pigsy and, upon the Dragon's removing the magical "water-fending pearls," the gate to the Crystal Palace vanishes. Monkey forces Pigsy to bring up the body, which, as Monkey confirms, has been for three years wonderfully preserved by the magical pearl. They return to the temple "to show him to Tripitaka." Pigsy, feeling "very ill-used" by Monkey "thought of a plan to revenge himself," which will make things worse for Monkey later when Tripitaka, tricked by Pigsy, gives Monkey a "head-ache spell."
In Chapter 21, despite the feud Pigsy carries on against Monkey, Tripitaka supervises while Monkey--with the power of Lao Tzu's "Nine Times Sublimated Life Restoring Elixir" from the "Trayaśimstra Courtyard of the heavenly palace of Quit Grief" in the "thirty-third heaven"--restores the king through the breath of life. 

Monkey stepped forward, and putting his wide mouth against the Emperor’s lips he blew hard into [the king's] throat.

The three, Monkey, Tripitaka and vengeful Pigsy (with Sandy also), take the true king, now called the "Emperor," on his journey back to Crow-cock. After an emotional entrance to the city (without the "five hundred priests in gorgeous procession, blowing conches"), the false king questions their papers and motives, though they are saved by Monkey's magic and by the prince of Crow-cock who speaks for them. Monkey now has his chance to triumphantly disclose that they have with them the true king and that the one on the throne is an imposter!

I raised him from the dead and restored him to life without hurt or harm. He earnestly begged to be admitted to our faith, and act as carrier on the road, to join with us in our quest and journey to the Western Land. The false king who sits on the throne is that foul magician; he that now carries our load is Crow-cock’s rightful king!

A battle ensues between Monkey and the shape-shifting wizard imposter, who turns himself into the image of Tripitaka. With the help of deities Monkey magically summons, he avoids slaying his priest master and pursues the imposter to the clouds, where a second recitation of the "head-ache spell" separates the imposter from the real Tripitaka. Just as Monkey is about to victoriously end the fight, Bodhisattva Manjuśrī appears commanding Monkey to stop. In a magic mirror Bodhisattva shows that the false king and wizard is really Bodhisattva Manjuśrī’s lion, which he rides upon.
Bodhisattva reveals that the true king had three years ago thrown a disguised Bodhisattva (disguised as a begging priest) into the river to die, but Bodhisattva had then been rescued by "a guardian spirit" after three nights. When he afterward complained to Buddha about what the king had done, Buddha sent the lion as a wizard to replace the king and throw the king in the well for three years as retribution. Monkey, now satisfied with the reason for the imposter's role and that the imposter never hurt anyone (including the king's wives), allows Bodhisattva to take the lion and leave.

‘Very well then,’ said Monkey. ‘Take him away. If you had not come just in time, he’d have been dead by now.’ Manjuśrī then recited a spell and said, ‘Creature, back to your true shape and look sharp about it!’ ... [Bodhisattva] Manjuśrī, putting down the lotus that he carried in his hand, harnessed the lion, mounted him and rode away over the clouds.

[Image: Wu Cheng'en (Ch'êng-ên) (United States public domain).]
https://www.britannica.com/biography/Wu-Chengen