Promise of Destruction

Promise of Destruction is a companion quest for Cassandra in Dragon Age: Inquisition.

"Cassandra has reason to believe that Corypheus is behind the disappearance of the Seekers of the Truth, but she requires help to prove it."

Acquisition
This quest becomes available after the conclusion of Here Lies the Abyss, by talking to Cassandra in Skyhold.

Walkthrough

 * Complete the War Table operation called Locate the Missing Seekers. A temporary zone - Caer Oswin - will be unlocked on the world map.
 * Travel to Caer Oswin with Cassandra in the party. Head towards the castle - the path is quite straightforward.
 * Enter the castle dungeon, where there will be some soldiers - apparently of the Order of Fiery Promise - waiting. Loot dungeon key on one of the soldier corpses and continue forward.
 * After exiting the dungeon and a fight outside, loot the courtyard key. There is a cutscene, where Cassandra wonders how the Seekers could fell prey to Corypheus and the Order of Fiery Promise so easily. After entering the castle, there are some more soldiers to fight. Codex entry: The Order of Fiery Promise can also be found there. When heading upstairs, the party will find Daniel, one of the Seekers. Another cutscene occurs, where Daniel explains that Lord Seeker Lucius is behind the disappearance of the Seekers as he has sold them to the Order of Fiery Promise.
 * Find Lord Seeker Lucius outside the castle. He will explain his motives for the betrayal, and reveal some facts about the Seekers. Lucius also gives Cassandra a book of the Order's secrets. After the cutscene, the final fight occurs. Clear and loot everything before exiting the area.
 * Meet Cassandra back at Skyhold after she has had time to read Lucius’ book. She will explain the Inquisitor some new facts about the Rite of Tranquility and also about possibly rebuilding the Seekers. This conversation unlocks Codex entry: Rite of Tranquility.

Rewards
Andrastian Chantry Throne