If you haven't gotten the Elder Scroll from the Main Quest line, check the quest "Elder Knowledge" in a guide for the main game. Otherwise, head to the College of Winterhold and buy the scroll back from Urag gro-Shub. Obtaining the scroll ends this quest. When you've got both scrolls, head back to the fort and talk to the Moth Priest.
Unbound Before the Storm Bleak Falls Barrow Dragon Rising The Way of the Voice The Horn of Jurgen Windcaller A Blade in the Dark Diplomatic Immunity A Cornered Rat Alduin's Wall The Throat of the World Elder Knowledge Alduin's Bane Season Unending Fallen The World Eater's Eyrie Sovngarde Dragonslayer
Loss of Innocence With Friends Like These Destroy the Dark Brotherhood! Sanctuary Mourning Never Comes Whispers in the Dark Silence Has Been Broken Bound Until Death Breaching Security The Cure for Madness Recipe for Disaster To Kill an Emperor Death Incarnate Hail Sithis!