The Fallen

This quest starts immediately after the quest Alduin's Bane is complete. However, it will be put on hold shortly after it starts for Season Unending if the Civil War questline is incomplete or not started.

Background
''After I defeated Alduin at the top of the Throat of the World, he fled from me. One of his dragon allies may be able to tell me where he's gone. With the help of the Jarl of Whiterun, I've trapped Odahviing in Dragonsreach. Odahviing revealed that Alduin's lair is located in the ancient temple of Skuldafn, which is only accessible by air. Odahviing has offered to take me there, in return for his freedom.''

Objectives

 * Learn shout to call Odahviing
 * Prepare the trap
 * Call Odahviing to Dragonsreach
 * Defeat and trap Odahviing
 * Interrogate Odahviing

Walkthrough
After you have concluded the peace treaty negotiation in Season Unending, you will learn that names of all dragons are actually Words of Power, and that Dragon Shouts can be used to call them. You will then receive the Words of Power for Odahviing, in order to lure him into the trap as negotiated with the Jarl of Whiterun. If you did not negotiate a treaty, these words can be learned from Paarthurnax at The Throat of the World or Esbern at Sky Haven Temple.

You can now spring the trap for Odahviing. Travel to Dragonsreach and confirm with the Jarl that you are ready. Exit through the doors behind the throne room, to the "Great Porch" (Esbern calls it, incorrectly, the "Courtyard"). From this large open area you can call Odahviing, using first his Dragon Shout, and then Dragonrend to draw him out of the sky. (Note: You may need to go up on the small balcony to the right and shout from there. When shouting, hold the button down for longer to complete the Call Dragon Shout.) Do not bother fighting him or trying to drain his power, as he is at this point invincible. Lure him into the enclosed area, and the trap will come down on his neck and hold him in place. He will then speak to the Dragonborn, and offer to take them to Skuldafn in exchange for his freedom.

Note: If your followers or NPCs insist on tanking Odahviing and keeping far away from the trap, attack him until he is "KO'd" and then retreat to the doors. When Odahviing's HP is restored (since he is not killable at this point), he should attempt to follow you and get trapped.

At this point, Farengar may come in and start running tests on Odahviing, with amusing results. When you choose to free Odahviing, a guard on the second floor will help you. Speak with Odahviing again, and he'll carry you to Alduin's portal to Sovngarde via a cutscene.

Trivia

 * If a Whiterun Guard is killed and thrown off the building you can still loot his/her body, by going to his/her last position.
 * You might need to hold down the shout button then release in order to cause Odahviing to come and complete the "Call Odahviing to Dragonsreach" section of the quest.