Trying to hide the big reveal

[Forte]

So I'm writing an Ice Age campaign and I finally got a plot outline I like, but I'm afraid it might be too obvious. My players are fairly clever and I do want there to be a kind of, "Aha!" moment, but I don't want it to be immediate. Here's the situation:

The main villian is going to be an elf woman and her followers. The plot is going to revolve around her discovering a way to force entry into the spirit world to steal its power since she's tired of her people being at the mercy of nature. There's of course backlash on the world and all of the races will eventually be involved in the conflict with her. The part where I'm trying to get the "aha" moment is that moving toward a conclusion, the party is going to have to chase her into a cavern system where she's trying to find a natural weak spot between worlds. She'll vow to search for eternity and whatnot in a the classic bbeg last words type speech and her followers (and her if she survives) will be exiled to stay underground. Currently, I have Aneloltheq as the bbeg's name.

So, given a group of fairly clever players (several of whom already have a fondness for drow), do you think they'd figure it out long in advance? If so, any suggestions on how I can hide it while still creating that, "Ah, should have seen it coming" feeling near the end?

[Bobmufin52]

Have the bbeg and her followers stay above ground for as long as posible.
Mabey have it look like the weakness between the two worlds is in a castle or fort, and when the PCs get to the room where they think the bbge is, have the room empty w/a secret passage leading to the actual area undergound.

[Myiven]

As long as you don't mention spiders or anarchy too much, you should be OK.

[Strawman]

Remember to have the villains act like regular elves. Even though they are creating the drow, the drow culture will not exist for a couple generations.

With something like this, the more relatable and complex you make the main villain, the harder it is to see what their actions will do. Over-the-top Disney-villains make it hard to be subtle.

Perspective can be incredibly different from person to person. The way someone describes the creation of the drow when it is happening and the way someone describes it three hundred years later are completely different. Just describe the events from the veiwpoint of someone who does not know what the long term effects will be, and even clever players will have a hard time figuring it out.