The so-called secret at the heart of The Feast of the Goat

For all the strengths of Mario Vargas Llosa's The Feast of the Goat and there are many - his uncanny sense of how a dictator manipulates and humiliates others to retain his power, the sense of how the dictator, Trujillo in this case but you could substitute any of many, Saddam Hussein, Idi Amin, Kim Jong-il (?), deludes himself into thinking that he has brought great prosperity to his land and that he is beloved by his people for bringing them freedom, the smart use of multiple time frames, the excellent building of narrative tension as we watch the plot against Trujillo slowly materialize, the subtle mixture of fictional and historical elements, the vantage of the present - woman's visit to her homeland circa 2000 after many years away, to cite just a few of its strengths - one thing does bother me, and that's how can a narrative work when we're smarter than the characters, and I'm not talking about the omniscient narrative point of view but the plot element in which I keep thinking that Vargas Llosa intends to surprise us but then I think, no, he's too smart for that, he knows we've figured out the "secret" long before the main character has, but why? The secret I'm talking about? - it's obvious to any observant reader - most readers of Vargas Llosa are observant, I would say - that Urania, the first character introduced, must be an illegitimate daughter of Trujillo, as all the elements fit - the disappearance of her mother, Trunillo's interest in her when she was a child, and most of all her father's horror when he'd learned that Trujillo's son was making a play for her. The real mystery is why she, a highly intelligent and accomplished woman, never figured this out. We'll see what use Vargas Llosa makes of this plot element.