Korra and Unalaq in “Unfinished Business”

Korra

So once we get to the South pole, then what happens?

Unalaq

You will open an ancient spirit portal.

Korra

I'm sorry. What now?

Unalaq

At the South pole, there is a portal that connects our world to the spirit world. But it has long been closed.

Korra

And that's why the evil spirits are attacking?

Unalaq

There are no evil spirits. There is light and dark in them all. But when they're unbalanced, the darkness takes over. If you can open the portal in time, balance will be restored.

Korra

What do you mean "in time"?

Unalaq

There's a reason the glacier spirits festival ends on the winter solstice. That's when the spirit world and the physical world are close together. Only then can the Avatar open the portal.

Korra

The winter solstice is tomorrow.

Unalaq

Exactly. And we can't afford to wait another year.