What Tony said. Gulliver's Travels is a travelogue, kind of a travel diary, so it had no overall plot. It's been a long time since I read it, but if there is a changing point, it would be near the very end. It's possible that Gulliver decides to stop traveling or is too old to travel any more; if so, then that could be what you're looking for. I'm pretty sure that he begins to take much better care of his horses, which makes some sense to us (though perhaps not to the extremes that he goes to), but it would have been considered ridiculous at the time Swift wrote the book.