The Legend of Korra, Book 3: Change

Lin Beifong:
I just got word from Lord Zuko and Tonraq.

Korra:
Why is Lord Zuko with my dad?

Lin Beifong:
Zaheer and the others have escaped.

Tenzin:
How is that possible?

Lin Beifong:
Because Zaheer is an airbender now.

Tenzin:
No.

Korra:
All right, hold on. Will you quit ignoring me and tell me what's going on? Who's Zaheer? Why is my life in danger?

Tenzin:
Shortly after we found out you were the Avatar, Zaheer and three others attempted to kidnap you. Luckily, your father, Lord Zuko, Chief Sokka, and I were there to stop them. We apprehended the criminals and locked them away in prisons designed to impair their abilities.

Korra:
So that's why you and my dad sheltered me away.

Tenzin:
It was for your own safety.

Mako:
Why were they trying to kidnap Korra?

Lin Beifong:
We spent 13 years interrogating them, but they never broke. To this day, no one knows what their motive was.