Often, the perception of good and evil depends on how much knowledge one has about an event or the person or persons involved in it. The more information one has, the fairer the judgement of who's right and who's wrong becomes.
In Frank L Baum's The Wonderful Wizard of Oz, all the information we get is from the perspective of a gormless farmgirl searching for a way home. Whoever can help her achieve her objective we think of as "good" while those who strew obstacles in her way have to be "bad". It's odd then that Dorothy's benefactor, the Wizard himself, would set the assasination of a rival as a precondition for his assistance, and we accept this morally reprehensible task without question. Means justifying the ends.
But the Oz in Gregory Maguire's revisionist novel, Wicked, is a far more politically complex world than the one Baum presents. The Wizard has usurped authority in the Emerald City from the ruling regent and has embarked on a campaign of eco-political expansion to take the whole of Oz under his control. There is little resistance at first as he seems to bring in wealth and prosperity to the people, but those he represses and exploits he keeps out of sight from the general population. He protects himself with a secret police called the Gale Force which enforces his interests with extreme prejudice on the periphery of polite society.
While there seems to be a growing resistance movement against the Wizard, the focus of Wicked falls on a lonely figure, an anomalous green-skinned girl whose cause is to end the oppression one way or another. But as one effort after another ends in failure, she retreats further and further away from society, and eventually becomes known as the Wicked Witch of the West more by reputation than by actual intent on her part.
When Dorothy arrives on the scene however, her bumbling around Oz destroys everything that Elphaba (aka WWW) holds dear, starting with Elphaba's sister who is crushed by Dorothy's far-flung farmhouse. Even so, Elphaba holds Dorothy no malice (well, perhaps only growing contempt, annoyance and frustration) but instead sees her as an opportunity to atone for past mistakes. But tragically, it is Dorothy's ignorant good intentions to help Elphaba that causes Elphaba's unglamorous death.
Wicked is a discussion on the nature of good and evil, examining the subject from the perspectives of religion, science, and magic. It looks at people's motivation for behaving the way they do, and questions the influence of choice, manipulation and ordination in people's actions.
Wicked puts an adult perspective on a simple children's tale. It fleshes out the relationships of the main players and pre-Dorothy histories in Baum's narrative. Given this additional knowledge, we realize that it can be all too easy to judge a book by its cover.