what does the necromancy of thay do

The Necromancy of Thay is a book found in the Blighted Village Apothecarys basement in Baldurs Gate 3. To unlock the book, players need to find the Dark Amethyst, a cursed gemstone that can be placed in the mouth of the book to open it. Once opened, players can choose to read the book or destroy it. If players choose to read the book, they will need to pass difficult Wisdom Saving Throws to unlock its secrets. Successfully unlocking the book grants the player the ability to cast Speak with Dead once per Long Rest, allowing them to have it permanently active. If players choose to destroy the book, they must attack it with Radiant damage. Destroying the book is not recommended, as it does not provide much of a reward.