Unlock the Ancient Tome is a sub-quest of Search the Cellar in Act One of Baldur's Gate 3. It is initiated upon finding the book "The Necromancy of Thay" in the Blighted Village.
 | Spoiler warning: The following content contains unhidden spoilers. Read at your own risk. |
Objectives
Objectives and journal entries may vary pending player decisions and outcomes.
- This book is locked tight, and the mechanism isn't shaped for a key. Maybe some kind of stone would work?
- The owner of the tome mentioned a keygem. Could this be the secret to unlocking 'The Necromancy of Thay'?
- The necromancer's apprentice mentioned a keygem lost in the tunnels. We need to find it.
- We found the gem to unlock the book.
- We've unlocked the book of necromancy. Should we read it?
- The tome is clearly powerful, but we'll need to read further to uncover all of its secrets.
- We managed to read most of the book, absorbing some of it's necromatic power, but it snapped shut before we could finish. There must be a way to read the end.
- We made it to the final page of the tome, but it's indecipherable. We need to find a way to read it.
- Mystic Carrion and his Spirits told us that we need the 'Tharchiate Codex' to unlock the true power of 'The Necromancy of Thay'.
- Mystic Carrion and his Spirits told us that we need the 'Tharchiate Codex' to unlock the true power of 'The Necromancy of Thay'.
- We've accessed the vault, and the lower level of Sorcerous Sundries. Now to find the 'Tharchiate Codex'.
- We have the 'Tharchiate Codex'. To decipher "The Necromancy of Thay', we need to first read the codex.
- We read the 'Tharchiate Codex', and now have the knowledge to finish 'The Necromancy of Thay'
Walkthrough
Unlocking the Book
The Necromancy of Thay is obtained during Search the Cellar within the apothecary's secret laboratory past the ornate mirror. Removing the book from its trapped room starts a quest to either unlock the Necromancy of Thay's secrets or destroy it forever. Retrieving the tome from the apothecary's cellar is only one part of unlocking it - it also requires a key to open.
There are two ways to find the Dark Amethyst needed to unlock the book. One way is to enter the blacksmith's basement north of the Blighted Village waypoint (this is also the same basement where Finish the Masterwork Weapon is completed). One of the northern walls is cracked and can be destroyed with force damage, which leads to the Whispering Depths. The other way is to investigate the well (X:23, Y:400) north of the waypoint. Choose "[INVESTIGATION] Peer into the well" and then climb the bucket rope ladder down into the well to arrive at the cave. Inside the cave is an Apprentice's Pack (X:-494, Y:-364) which has more information on the stone's whereabouts. It's deeper within the cave. The Dark Amethyst is in the western area of the cave (X:-563, Y:-353) below a Spider Matriarch's webs. Either sneak past the horde or spiders, or defeat them all. Defeating the matriarch grants Poisoner's Robes.
Reading the Book
With both the Dark Amethyst and the Necromancy of Thay in the party's inventory, click on the Necromancy of Thay. This starts a dialogue with the party inspecting the tome. Select 'Place the amethyst in the slot on the book's cover' to unlock it.
From here, you have several options:
- Open the book and read it
- Give the book to Astarion or Gale
- Drop the book and proceed with Destroy the Ancient Tome
If you choose to open and read the book, you must pass three Wisdom saving throws to avoid being cursed. See the Necromancy of Thay page for full details on this interaction. Turning at least one page of the book grants the Speak with Dead spell and the Forbidden Knowledge buff. Once you've passed all three saving throws, the book snaps shut. It has one more secret to reveal, but you must first reach the Lower City in Act Three to unlock its full potential.
Choosing to give the book to Astarion grants approval points from him and a special cutscene at camp.
Fully Unlocking the Book's Secrets
More hints - not mandatory - about the Necromancy of Thay can be found throughout Act Two and Act Three:
- In the Silent Library within the Gauntlet of Shar, one of the books refers to a Tharchiate Codex that can unlock the tome's true power.
- A book on necromantic tomes on the rooftop of Moonrise Towers also makes reference to the Tharchiate Codex.
- By speaking with Mystic Carrion in the Lower City of Baldur's Gate, you can learn that Sorcerous Sundries holds the Codex in its lower vaults.
Once you've reached the Lower City, proceed to the Sorcerous Vault. You'll find 
in the Elminister section of the Vault, which can be unlocked by opening doors in this order: Silverhand -> Evocation -> Wish.
Note: If you previously gave Necromancy of Thay to Astarion or Gale, they must be the controlled character and also hold in order to fully comprehend the text and unlock its secrets.
Read , which will curse you with (see the Codex's page for full details). Finally, read Necromancy of Thay once more and pass one last DC 20 
Wisdom saving throw to receive 
and complete the quest.
Rewards
- 80xp
-
Notes
- Gale can technically consume the Necromancy of Thay book, which destroys it without granting any of the abilities or knowledge. He can also read it like normal, if the item is sent to his inventory and he reads it while being the controlled character.