Defeat Ketheric Thorm

Ketheric Thorm has retreated into the heart of Moonrise Towers.

Defeat Ketheric Thorm is a Quest in Act Two of Baldur's Gate 3. It can be started by completing  Infiltrate Moonrise Towers.

Objectives

Objectives and journal entries may vary pending story decisions and outcomes.

Follow Ketheric.

• We battled Ketheric Thorm. Before we could finish him, he fled somewhere below the tower. We need to follow him.

Escape Balthazar's lab.

• Ketheric learned that the weapon he's searching for and the artefact we carry are one and the same. We've been teleported to a laboratory where Balthazar plans to remove us from the artefact's protection. We need to escape.

Search the Colony for Ketheric.

• We pursued Ketheric beneath the tower and found ourselves in what appears to be a mind flayer colony. We need to find him.
• We escaped Balthazar's laboratory and found ourselves in a mind flayer colony. We need to search for Ketheric.

Kill Ketheric Thorm.

• We found Ketheric, along with a Bhaalist named Orin and a Banite called Gortash. They brandished a triad of magical stones that seem to give them control over an illithid elder brain. Orin and Gortash have taken the brain to Baldur's Gate aboard a nautiloid - leaving Ketheric to face us.

Obtain Ketheric Thorm's Netherstone.

• Close to death, Ketheric transformed into an apostle of the dark deity Myrkul - and was defeated all the same. We should search his body for the stone he used to control the elder brain.

Quest Complete

• The gem we found on Ketheric's body is a Netherstone - one of three used to control the elder brain. Orin and Gortash carry the other two. If we want to cure ourselves and save the Sword Coast, we'll have to hunt the pair through Baldur's Gate and claim each of their Netherstones in turn.

Walkthrough

Map of the Colony.

Introduction

Depending on the party's actions in  Find Ketheric Thorm's Relic and  Resolve the Abduction /  Capture Isobel the Selûnite Cleric, the party's state after going on the rooftop of Moonrise Towers is very different.

If the party worked with Balthazar and sent the Nightsong to Ketheric Thorm and Isobel was kidnapped or killed, then the party stands judgment before the Absolute and is taken to Balthazar's Necrotic Library after Ketheric Thorm realizes the party possesses the Astral Prism. When the party comes to, they are trapped in Profane Wombs and must escape before Balthazar can complete the ritual. After escaping, Balthazar must be defeated. He is joined by several undead servants. If the party killed Dror Ragzlin and Minthara, then their undead corpses are among them.

If the party saved or killed the Nightsong, then Ketheric Thorm fights the party on the rooftop and, before his hitpoints are fully depleted, a tentacle bursts out from the tower and causes him to disappear. The party must follow him down the Hollow Tower and into the Mind Flayer Colony.

The main objective of this quest is to reach the Necrotic Apparatus northeast of the Necrotic Laboratory. It is mandatory to use the necrotic apparatus to descend to the heart of the colony where the last battle with Ketheric Thorm will be fought.

Locating the Chosen Three

Thorm becomes the Apostle of Myrkul.

Once the party has located the Neural Apparatus on the eastern end of the Colony, they must descend to face Ketheric Thorm. Next to the Apparatus is a restoration pod that grants the party all the benefits of a long rest in preparation for the final confrontation. After descending and opening the door, a scene plays which reveals that Thorm is joined by two collaborators - Gortash and Orin the Red - as well as a captive Grand Duke, Ulder Ravengard. The trio use Netherstones to control an Elder Brain with a Netherese crown. If Gale is in the party, he must be talked down from sacrificing himself by detonating his Netherese Orb, otherwise the game ends early with an ominous note that mass-ceremorphosis has occurred all over the Sword Coast.

It necessary to approach Ketheric Thorm, who threatens the party. There is one last chance to speak to him. By using a Persuasion check (DC 18), he can be talked down somewhat, which results in Ketheric Thorm thrwoing himself into the pit and transforming into the Apostle of Myrkul, which must be defeated then. Otherwise, Ketheric Thorm will fight the party to the death first. If the Aylin was captured or freed, she will be there, too. Aylin must be freed by using the help action. Additionally, if Isobel was kidnapped, she also will be there, and fight on her father's side against the party. After almost defeating Ketheric Thorm, he falls into a pit and transforms into the Apostle of Myrkul. Defeating it will result in Myrkul abandoning Ketheric Thorm, who finally dies. The party must take his Netherstone and go to the portal to return to the ground floor of Moonrise Towers.

Optional activities

The following activities are not strictly required to complete the quest, but can offer additional insight, loot, and permanent buffs.

Recruiting Us

If Us was recruited on and survived the Nautiloid, they can be found in the Morgue, caged by a creature named Chop. The party can stealthily lockpick the cage's door (DC 14) or attempt to persuade Chop to free Us. The party can use an Illithid Wisdom check (DC 14), a Persuasion check (DC 14), or an Intimidation check (DC 18). Failing the check makes Chop hostile.

Slack-Skinned Head

Off to the side of the Necrotic Laboratory is a Slack-Skinned Head. Combining a brain jar with the machine next to the head allows the mind to speak. Most of these heads are simply stories of victims of Gortash, but the Waking Mind is the mind of a Githzerai that knows it is trapped. It offers to provide a Githzerai Mind Barrier to the party if they agree to free it. If agreeing, the party member that frees the mind gets a permanent  Githzerai Mind Barrier buff.

The locations of the minds are as follows:

• Butchered Mind - in the Morgue on a shelf at X: 678 Y: -68
• Closed Mind - in the Barracks in Ironfingers' room at X: 716 Y: 34
• Fresh Mind - on a box near the elevator to the Thorm fight at X: 750 Y: -8
• True Mind - right in front of the machine at X: 696 Y: -116
• Waking Mind - in the Necrotic Laboratory behind the door locked by the mind puzzle at X: 749 Y: -138
• Willing Mind - on the shelf next to the machine at X: 693 Y: -115

Additionally, the Dark Mind and Slave Mind from the Prologue can be used here.

Mind puzzle

A combination for the mind puzzle.

The Mind Puzzle is on the southern end of the Necrotic Laboratory X: 737 Y: -112. A party member must choose to connect with it to start the puzzle. The puzzle involves connecting the various senses on one side to the corresponding sense on the other side of the nodes. Completing the puzzle opens up a locked door which contains the Waking Mind and the Blade of Oppressed Souls. There is also a Desecrated Relief that sheds more light on the Grand Design.

Freeing prisoners

Within the Tadpoling Centre, a number of not yet infected prisoners can be set free, at the risk of also releasing a number of Mind Flayers. This is part of  Find Zevlor. North of the prisoners is the captured Mizora, Zariel's asset, who can be freed as part of Wyll's companion quest,  The Blade of Frontiers.

Kressa Bonedaughter

Kressa Bonedaughter is in the Barracks, giving a speech to Hairy Henry, Ironfinger, and Maghtew Budj. If getting to close to her, she calls the party out as most likely being intruders. She can be talked down with a Deception check (DC 21) or fought against. For Dark Urge characters, there is unique dialogue with Kressa that reveals more about their past life, but a fight is unavoidable with her specifically for this origin.

Quest rewards

• Ketheric's Netherstone
• Ketheric's Shield
• Ketheric's Warhammer
• Reaper's Embrace

Achievements

No Free Lunches

Defeat the Apostle of Myrkul before it consumes any necromites.