The following contains spoilers for Wicked: Part 1, now playing in theatersThe Grimmerie is one of the most important artifacts in Wicked: Part 1, and has a vital role to play in the overarching story of Elphaba. Adapted from the Broadway musical of the same name (which was in turn based off the novel by Gregory Maguire), Wicked tells the story of how the well-intentioned Elphaba becomes the Wicked Witch of the West from The Wizard of Oz. A major aspect of her journey centers around the Grimmerie, a powerful spellbook that appears in all three versions of the story and factors heavily into secrets about Elphaba’s past, present, and future.

https://screenrant.com/wicked-grimmerie-book-explained/