Warning: SPOILERS for both the A Wrinkle in Time book and movie are ahead!
A Wrinkle in Time is a book that countless people have loved in the decades since its publication. As such, there are certainly many who are excited that the novel is now a theatrical film for the first time ever. Of course, no previously existing material makes the jump from page to screen entirely intact.
There are several interesting changes that have been made to the source material for Disney's new movie. Some are small, some not so much. Here's a rundown of the most significant changes made to A Wrinkle in Time.
The movie opens with backstory. We first see Mr. Murry and a young Meg spending time together in his lab before they first meet the new baby who will be Charles Wallace. The book opens on a dark and stormy night. In fact, it opens with that exact line. Reese Witherspoon makes reference to it when we first meet Mrs. Whatsit. We also get additional backstory later in the movie that never shows up in the book, as there are no scenes in the book that don't include Meg and come from her perspective.
Charles Wallace is adopted. Charles Wallace is one of the more interesting characters in A Wrinkle in Time, as he's barely more than a toddler, but is highly intelligent. That intelligence is a key part of the plot, but the source of that intelligence is never made entirely clear in the book or the film. It's hinted at in the book that this may be due to some genetic differences that he has, but in the movie, the fact that he is so unlike the rest of his family is explained by the fact that he isn't biologically related to them; he's actually adopted. It's unclear why this change was made as it's not particularly necessary. It may have been done simply to explain the diverse family make-up due to casting or to broaden the idea of what makes a family.
The Mrs. Don't Know Where Mr. Murry Is. In the film, the three Mrs. find Meg and her brother by following Mr. Murry's pleas for help to their destination, but they don't actually know where they are coming from. The characters jump from one world to another in an attempt to follow his path. In the novel, the women are all perfectly aware that Mr. Murry is trapped on Camazotz. The "tessering" from planet to planet in the novel is only done to make the process easier on the children, who have never done it before, and thus a single jump to Camazotz would be unwise. With each jump, they get closer to their destination, making the final leap easier.
Calvin trusts the Mrs., Meg Doesn't. The most significant changes revolve around the sort of character Meg is. While she does have a character arc in the book, it's much stronger in the movie. In the film, she's not entirely sure if she trusts the women, being the most hesitant to leave Earth. In the book, she trusts them, with the novel specifically saying that she instantly had a feeling of trust in Mrs. Which specifically. Instead, Calvin is the one who is suspicious of them and isn't sure they should be trusted, though he does come around.
Mrs. Which Is Visible. In the film, the role of Mrs. Which, the most powerful of the three women, is played by the great Oprah Winfrey. If the movie had been closer to the book, you really only would have heard her. Mrs. Which spends most of her time in the book existing only as a disembodied voice, only rarely taking any sort of corporeal form. The movie hints at this idea by making her initially appear much too large because she doesn't know what size to take, but she doesn't seem to have difficulty with the concept of having a form.
The Happy Medium is a dude. Of all the changes to characters between the book and the movie, none is more striking than casting Zack Galifianakis as the Happy Medium. Primarily, this is because the character in the book is a woman. The Happy Medium also is a fairly simple character who uses a crystal ball to scry information, rather than requiring everybody to have perfect balance while they hold hands. Meg has no issues with the Medium and doesn't require any special attention in the book.
Meg forces the "tesser" to Camazotz. As previously mentioned, in the novel, Mr. Murry's location is known from the beginning, so the goal of sending the children there to rescue him is always the plan. In the book, it's not until they visit the Happy Medium that they discover where he is. The Mrs. then want to go back to Earth to work on a new plan with Meg's mother, but Meg is able to use her own mental strength, intentional or otherwise, to force the trip to Camzotz. This leaves them without the help of the Mrs., but in the book, the women ditch them anyway.
Camazotz is a place where what you see isn't real. The name Camazotz is used interchangeably with the evil that emanates from it in the film. In the book, however, Camazotz is clearly a planet, it just happens to be the one where The IT resides. In the novel, the kids travel from the subdivision with the synchronized ball bouncing, into the heart of a city, where they find and enter the CENTRAL Central Intelligence building. In the movie, the subdivision transforms before their eyes into a beach before transforming again into Mr. Murry's prison. For the purposes of the film, it doesn't appear that the kids bouncing balls or the red-eyed man are actually people; rather, they're creations of the mind of The IT. In the book, Camazotz is a planet of humans who have come under the sway of the IT and have chosen a life of conformity under IT's control.
Mr. Murry Is Able To Tesser Home. While Chris Pine's Mr. Murry isn't an expert on being able to travel across the galaxy in the blink of an eye, when he needs to do so in the movie, he's able to use the ability to get home. However, in the book, he's really not very good at it, and he actually transports himself, Calvin and Meg to an entirely new planet where Meg is nursed back to health by an alien she dubs Aunt Beast. She ends up getting into a serious fight with her father for leaving Charles Wallace behind before she goes back to Camazotz alone to get him. The film skips this section of the book entirely, jumping directly from the first confrontation with The IT to the last.
There's a lot more action. While A Wrinkle in Time isn't without its big moments in book form, it doesn't have nearly enough action for your standard studio tentpole. To this end, there a couple of action sequences in the movie that don't appear at all in the book. First, Calvin falling from the back of Mrs. Whatsit and being saved by the sentient flowers never happens. Also, the flower characters don't exist. Secondly, the sequence on Camazotz where the field becomes a forest and the characters are chased by a storm never happens. They arrive on Camzotz without incident.