Wicked - The Life and Times of the Wicked Witch of the West by Gregory Maguire

Don't make the mistake of thinking this is like the musical. The plot is VERY different and it doesn't focus as much on the friendship and potential slashy relationship between the good witch Glinda/Galinda and Elphaba. That said, there IS still an undercurrent of something happening between Glinda and Elphaba, but don't expect anything explicit in regards to those two.
If you've seen the musical first, as I had, you might be a little disappointed with the ending. The musical seemed to have a far neater integration with the original Wizard of Oz film and the characters that are mentioned throughout the book and the original film. But it's still an interesting read. Partly because you spend most of the book wondering just what is the relationship between Glinda and Elphaba and what potentially may happen between them and to them.
Interestingly, the musical focuses far more on the love triangle in regards to Fiyero, and if anything the book reveals that he had a far less important role, at least in regards to Glinda/Galinda.

"Glinda was too fussed to listen that closely. The Witch in fact alarmed her a little. It was not just the novelty of seeing her again, but the strange shade. Also there was the thrill, basis indeterminable, which made Glinda shy, and caused her to rush her words and to speak in a false high voice like an adolescent. How quickly you could be thrown back into the terrible uncertainly of your youth!
For when she chose to remember her youth at all, she could scarcely dredge up an ounce of recollection about that daring meeting with the Wizard. She could recall far more clearly how she and Elphie has shared a bed on the road to the Emerald City. How brave that had made her feel, and how vulnerable too."

That is about as slashy as it gets though and it does tug at the heartstrings to know that inevitably these two may have messed up the one good thing in their lives - each other.

If you haven't seen the musical OR read the book, I personally would recommend both. I saw the musical in London with Idina Menzel when it opened in the UK and it had me in tears at the end of it (although the people I was with who were gay men and hadn't seen the original movie didn't like it in the slightest - so possibly more of a chick flick musical, if there is such a thing).

Gregory Maguire's official website can be found here: www.gregorymaguire.com/

-The US Wicked musical website is here: www.wickedthemusical.com/
-The UK Wicked musical website is here: www.wickedthemusical.co.uk/
-Purchase the book Wicked - The Life and Times of the Wicked Witch of the West by Gregory Maguire from US Amazon
-Purchase the book Wicked - The Life and Times of the Wicked Witch of the West by Gregory Maguire from UK Amazon