There are a lot of great moments in the ESO stories, but this one has always been my favorite because of the way a side branch of a main quest introduced a new objective to the main quest in the most utterly casual way:
(This is paraphrased because it's been a while)
Vanus Galerion: I did it! I destroyed the Great Shackle! The Planemeld is no more!
Cadwell: Jolly good! And as soon as you stop the planar vortex, everything will be right as rain!
Vanus: The what now?