So Tripitaka has to stay and make up the numbers while Monkey goes to try and return the missing 'Sorosvati.' Matters are complicated when this fake goddess turns out to have a single magic power - the ability to make men fall in love with her - and works this on Pigsy, Sandy and Yu Lung (who fight each other for her) and then Monkey himself.
Monkey offers to stay behind with the other six gods to give Tripitaka and his new love both their freedom, but then the real Sorosvati intervenes. This is a Deus Ex Machina ending, but it makes a change that the Deus in question is not Monkey for once. It also helps give the story an air of authenticity, when I consider how many of the old Monkey stories finish with the intercession of gods, celestials or even Buddha.