Nericon's Wrath is a Divinity II: Flames of Vengeance quest received from Nericon, the magical tree in Aleroth that kills passers-by indiscriminately on the undead-infested side of the barrier dividing Mardaneus Plaza. This quest is assigned when it allows the Dragon Knight to pass, permitting access to the city's Crow's Nest district.
Head into the Crow's Nest and find the Forgotten Crypt at the end of the first street.
Skulk the troll will greet you inside. Mindread him for 15000 exp to hear him chant some strange words. If you mindread Skulk every time you meet, you will be able to disable the trap on the Source Square door without sacrificing Abbott. Make your way through the fire and pull the lever to open the door. Skulk will appear to taunt you again. Follow him through the next set of traps and pull the next lever. When you get to the next door, pull the lever to open it.
Jump onto the platforms to avoid the poison and pull the lever on the third platform. Jump down and head through the unlocked door to meet Abbott.
Follow Abbott out of the room and head to the other door which was previously locked. Skulk will appear again, and a dialog will ensue with Abbott in which he declares there is no way to get past the deadly trap on the door without sacrificing himself. Choose what to do to get the door open. (If you've mindread Skulk each time you've spoken to him, then you don't have to sacrifice Abbott, he can cast the spell that Skulk was thinking of.)
Head into Source Square. Go up the stairs and down the hall and the Engineer will appear. You will be shown a cutscene and Behrlihn will offer a hint at what you need to do. There is no specific order to pulling the levers. Once all of the devices are deactivated and the minions are dead, battle the Engineer and loot the Engineer's Sword for Clue IV of To Find a Wizard following his death. Return to Nericon.