As soon as you accept the quest, turn around to find Tobias standing at the front door of the building.
On accept:
Tobias Mistmantle says: Let us go at once. We will track Sylvanas down. For Gilneas!
Follow Tobias Mistmantle into the Cathedral District.
Tobias runs out the front door and around to the canal separating Greymane Court and the Cathedral District. ([36.5, 54.0]
)
Tobias Mistmantle says: Let's do our best not to be seen, <name>.
Tobias jumps across the canal then runs to the wall to the northeast to eavesdrop. ([40.0, 31.0]
)
Tobias Mistmantle says: Did you hear that, <name>? Sylvanas is headed to the cathedral. Let's hurry!
Tobias runs into the cathedral and jumps into the water on the south side of the room. ([44.6, 51.6]
)
Tobias Mistmantle says: Quick! Hide in the water!
Sylvanas, Crenshaw and Warhowl all walk in the cathedral.
General Warhowl says: It appears as if you're losing control of Gilneas, Sylvanas. Garrosh fears he's going to have to carry out this invasion himself.
Lady Sylvanas Windrunner says: You can assure Garrosh that this is a minor setback. Our victory in Gilneas will be absolute.
General Warhowl says: You sound very confident, your Majesty. I seriously hope you do not plan to use the Plague. Garrosh has explicitly forbidden it.
Lady Sylvanas Windrunner says: You'd do well to watch your tone, General. Neither you nor Garrosh have anything to worry about. We've ceased all production of the Plague, as he ordered. We'd never deploy it without his permission.
General Warhowl says: I will deliver my report to our leader, then. By your leave, my lady.
Lady Sylvanas Windrunner says: Go with honor, General.
Warhowl exits the cathedral.
High Executor Crenshaw says: My Lady! Should I order my men to stop development of the Plague? Or are we to continue as planned?
Lady Sylvanas Windrunner says: What kind of question is that? Of course we're deploying the Plague as planned! Let the Gilneans enjoy their small victory. Not even their bones will remain by tomorrow.