The packaging of this book is very thriller-y, and maybe that's how everyone would slot this book, but I don't think it's really a thriller. It's more like a typical newspaper political sex scandal that is recounted in novel form.
There are a few minor or middling revelations that come toward the end, but I don't think there's anything in this that would count as a "big revelation" in the sense of something that would "rock your world."
Basically every chapter is told in the voice of a different character, either "now" (2016/2017/2018) or years ago at Oxford University circa 1992. So you see their different characters, outlooks, and psychologies, and that also helps to reveal more and more of the plot as you go along.
I don't think anyone in the book ever peeks and lurks about like the woman in the cover illustration--that's purely to give this book a thriller "look." But it's basically not a thriller. It's a legal/political novel.