So there are three demons, colour-coded and called "Red," "Blue" and "Yellow," who take it in turns to lose a fight with Monkey while appearing - to Tripitaka, Pigsy and Sandy - to be a girl, and old woman, and an old man respectively. Tripitaka then thinks Monkey has murdered them in turn and punishes Monkey by sending him away to his mountain of flowers and fruit.
It's not clear how Tripitaka perceives Monkey's fights with the demons, but presumably he doesn't see them fighting at all, or else it would be obvious that something was up. Suffice to say that Monkey is proved right only after he has been banished, when the Yellow demon captures Tripitaka.
The priest is only saved from being eaten when the demons double-cross each other. The Yellow demon is the most human of the three and he has a wife and daughter. Red and Blue kidnap Yellow's family and force him to exchange Tripitaka for their freedom.
By the time the exchange takes place Sandy has persuaded Monkey to come back and help, and they rescue Tripitaka. Yellow takes a fatal wound saving his family and dies in their arms having sacrificed himself.
I think this may be a difficult one to like without a better understanding of the Buddhist philosophy underpinning the concept behind the demons in this story - how they were created from Tripitaka's own repressed desires, and how they can transcend their origin to become human in some ill-defined (at least in the episode) way.
Or maybe it's just not a very gripping or involving story, with three particularly silly-looking monsters, even by Monkey's standards.
Possibly the best bit is a scene where Monkey's magic wishing staff disappears between shots, leaving the Narrator to explain that it "did eventually catch up with him."