Raubahn has outlined the plan of attack, and the Scions are to focus on rescuing Krile.
This quest is available if you have completed the quest Upon the Great Loch's Shore.
Starting the Quest
Talk to Alphinaud in The Lochs to begin the quest. There will be a cutscene.
Speak with Lyse
Check on the Aetheryte to attune to it if you have not yet done so. There will be a glow around Lyse, indicating an instanced battle. Check on her and the battle will ensue.
Solo Duty: The Key to Victory
Follow Wiscar. Defeat the Soblyns along the way, then continue following Wiscar. Check on the Queer Device on the other side of the building that Lyse is standing near. Go northwest to Wiscar and defeat any enemies attacking him, then help him and the others defeat the remaining enemies. Afterward, check on the Tattered Diary near Thancred.
Afterward, go south and the others will follow. Your destination is the Sali Monastery, which you can see to the southeast on the map. You can stay near the east wall to avoid the magitek at first, but you might be unable to avoid some fighting farther ahead.
When you get close to the monastery, you find a Magitek Avenger tethered to two Magitek Shield Generators. Destroy the shield generators as quickly as possible, then defeat the Magitek Avenger E1 quickly. You will get stacks of Vulnerability Up status the longer you take to defeat it.
Go through the gate behind where the Magitek Avenger was and check on the sparkling Destination. There will be a cutscene.
Speak with Lyse Again
Talk to Lyse again to complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Lyse to accept the next quest: The Resonant.