Desperate Yearnings: Zuko

A prequel to the End of the Avatar Cycle:

It's been twelve years since my wife's encasement. My children have grown but I feel a hole still in my heart. My mother... She has disappeared from my life and I want to find her. I will bring the Gang and my dear wife with me. I must find her...
Where has Queen Ursa been? Is there a secret Kyra had been keeping? Can Kyra contain herself from not seeing her children?