The Consulate is located on Arx. The building is on fire. Speak with the paladin that stands near the entrance and offer your help.
Inside, you will find Undead Lizards. They can regenerate as along as Cursed Fire stays on the battlefield. This means that you must focus on eliminating it. Using Bless is the best option.
Your goal is to reach the garden. In order to reach it you must go through 3 pairs of doors. A key to one of them is in the office located in the opposite side of The Consulate. The rest of the doors must be opened by using Thievery.
Reach the garden and use Spirit Vision to see a portal. Interact with it and you will be moved on an arena.
There, you must face Alexandar, Malady and Wendigo. This is a challenging fight and the main reason for that is the fact that enemies can resurrect as long as Black Mirrors are present on the arena. You must destroy all of them, otherwise, a portal that leads to another place won't open.
Warning: There is a way to make this quest easier. Alexandar, Malady and Wendigo will only appear if you leave the circle on which you appeared. If you have an archer, you can use them to destroy all Black Mirror from where you are standing. After that your enemies will appear only once. Then, you must go through a portal.
You reach a place where a few Lizards are guarding The Glowing Door. You can try to convince them to give you a key to the door or you can face them. Both options give you The Glowing Key which allows you to go through the door.
Enter inside and meet with Sadha.
Choice 1: Kill Sadha
The meeting ends with a fight with Sadha and her servants. Then, you must go through another portal and reach The Consulate's garden again.
Reward: 676,975 experience points
Choice 2: Free Sadha
This option is only available if you have Swornbreaker. This weapon can be found, e.g. in The Vault of Linder Kemm. It is held by a statue that stands in the room where Lord Arhu is imprisoned. This allows you to avoid the fight.
Reward: 134,750 experience points+ 4 guaranteed rewards + 1 out of 3 to choose from depending on your character class + Circle Of Suns