Even the most devout readers of George R.R. Martin's "A Song of Ice and Fire" book series were surprised by how some aspects of the Red Wedding played out (it should go without saying that spoilers abound from here on out in this article), and were handed yet another reminder that HBO’s adaptation of the epic fantasy novels isn't always going to stay true to the source material. But while season two took a few liberties (Daenerys's dragons getting kidnapped, for instance), this past season shuffled even more timelines, amalgamated even more characters, and twisted even more plot points as the one-book-per-season pace was pushed out the window like an overcurious Stark brat. Most changes involved simplifying and condensing Martin’s intricate narrative, but in some instances, the alterations served to enlarge the scope. We could quibble about some of the smaller changes that ultimately fulfilled the same function (Vargo Hoat’s rechristening as Locke, for example) or the shifting reasons behind certain events (such as the mutiny at Craster's Keep, which seemed more spontaneous than planned). But the changes we’re concerned with here are the ones that will affect the story going forward. Let’s take a look at the biggest Games-changers of season three. (Sorry, Ros!)
In the books, Robb's wife is named Jeyne Westerling, and she never does manage to get pregnant with a Stark child. She also survives the Red Wedding because she isn’t in attendance; it was decided that she should sit that one out, so as not to slight the Freys any further. A crucial point not addressed in the show is that Jeyne's family members are Lannister bannermen and that, at the behest of Lord Tywin, her mother had been giving Jeyne poisons to thwart pregnancy. After the Red Wedding, she is pardoned by the Iron Throne and instructed not to marry for two years to ward off any speculation if she were to have a child. Still, even though Talisa comes from a family with no political ties to Westeros, killing her and her unborn Stark baby off at the Red Wedding fulfills the same plot function, namely that Robb leaves behind no heir to Winterfell.
Because he was unable to knock Jeyne up despite their incessant shagging, and because his younger brothers Bran and Rickon were thought to have been murdered by Theon Greyjoy and his sister Arya is presumed dead, Robb had been considering legitimizing Jon Snow in the days leading up to the Red Wedding. The rationale was sound, as the move would have ensured Robb not only that a Stark could inherit the title of King in the North in the event of his untimely demise, but also thwart Tywin's maneuver of putting Tyrion next in line to inherit Winterfell by forcing him to marry Sansa Stark. Of course, Catelyn shot Robb's idea down. On the show, this topic never comes up.
In the books, there is a lot of foreshadowing about what was going to happen at the Red Wedding and about whom Walder Frey's real allies were. Roose Bolton's page is a Frey. The Lannister boys who were Robb's prisoners were related to the Freys. Roslin Frey can't stop crying during the wedding ceremony. The musicians were really awful, indicating that they weren't actually musicians. All of this, in addition to what was shown in the episode, helped set the stage for Walder Frey's betrayal. One thing that isn't addressed on the show is that the Freys never intended to kill Catelyn; it was only after she went mad upon watching Robb die — tearing at her face, laughing hysterically, holding hostage the least valuable member of the Frey household (a half-wit grandson nicknamed Jinglebell, not Walder's wife) — that the Freys decide that they have no choice but to kill her, too.
Like Bran, she's supposed to have a connection with her direwolf, the long-lost Nymeria, but that aspect of her personality is never broached on the show. This could become potentially important, as, in one of her nightly wolf dreams, she pulls the dead body of a certain character out of the river after the Red Wedding, which foreshadows the surprising epilogue to A Storm of Swords, the third book in the series.
In the books, there are two surviving bastards of King Robert: Gendry and Edric. Only one of these (Gendry) is introduced in the HBO series and their respective story lines have been conjoined. So it's Gendry, not Edric, who is taken to Stannis for a little bloodletting. Also, Gendry never learns that his father is King Robert in the books. And he doesn't set off in a rowboat toward King's Landing as he does in the season-three finale, a potentially huge departure from the novels, as it leaves open the possibility that he could become a legitimate player for the Iron Throne in future episodes.
The red priestess Melisandre never leaves Stannis's side in the books. Therefore, she never meets Arya and she never intuits that the red priest Thoros of Myr is blessed with the ability to resurrect the dead.
The Kingslayer returns to rescue Brienne from the bear pit because of a dream he has about her — but despite their pairing up for mutual survival, he doesn't seem to be as infatuated with her in the books as he is on the show. Also, his homecoming to King's Landing happens much later in the books than it does on the show, after some key events that have yet to occur on the show and that directly alter Cersei's mind-set when the sibling-lovers are reunited.
On the show, the prostitute-in-disguise professes her romantic love for Tyrion and her loyalty for Sansa, and is torn apart by jealousy and duty after Tyrion and Sansa marry (oh, the drama!). But in the books, Shae doesn't care quite so much; she doesn't consider "a little girl" to be a rival for Tyrion's affections, and is a bit more mercenary in general than how she's depicted on the show. She seems happy to consider any potential uptick in status presented to her, be it jewelry or promises of houses and servants. If someone had handed Shae a sack of diamonds and asked her to sail far, far away, as Varys does on the show (but not in the books), she likely would have accepted and jumped aboard the next ship out of town.
A fool who is friends with fools, Sansa clings to fairy-tale dreams despite all evidence to the contrary. When it's suggested she marry a Tyrell, she assumes it would be Loras — even though he is a member of the Kingsguard and cannot marry. When it turns out that her intended match is Loras's crippled brother, Willas, she's disappointed — even though marrying him would be her ticket out of King's Landing. More crucially, though, she is unaware of her impending wedding to Tyrion until the day of and is supremely petulant during the ordeal, even going so far as to refuse to kneel so that he can place the cloak on her; her pal Dontos the fool becomes a human footstool for Tyrion instead. Tyrion tries to get Sansa to accept him as her husband, but she can only see a deformed imp. She acts like a child and pouts like a child in the books, probably because, in the books, she is in her early teens.
Osha and Rickon
These two parted company with Bran, Hodor, and the Reed kids long ago as far as the timeline in the books is concerned; their journey is told off the page. Readers never learn much about Osha's past (Bruni who!?) and don't find out where she has taken Rickon until book five, and then only through hearsay. On the show, they've just set off for the Last Hearth, the stronghold of the Umbers.
Bran and the Reeds
"The raven is you" is a line created for the show, and it doesn't quite mesh with what we know so far in the books. The three-eyed raven is an entity of some kind, and isn't that why they're going beyond the Wall, to find it? Jojen also does not have epilepsy-like seizures with his visions and he doesn't enter Bran's dreams.
In the novels, he tells Mance Rayder that he deserted the Night's Watch and joined the wildlings for reasons relating to his being a bastard and never feeling fully accepted by his family — which becomes all the more poignant when, in the parallel story line occuring to the south, Robb is considering legitimizing him and making him a full Stark. Jon's relationship with Ygritte is also more of a true love story on the show than it is in the books; she knows an awful lot (as she repeatedly informs Jon), but one thing she doesn't know is that he's secretly still loyal to the Watch, and she doesn't seem to think that it's the two of them against the world.
She's a little more ruthless in the books, and prone to surprise attacks under the guise of hospitality herself. She tells the leader of a mercenary company that he has a day to consider an offer and gives him and his men wine, but she only does so to get them drunk for a sneak attack she has planned later that night. Also, Jorah Mormont is more explicit in his feelings for her, which causes problems down the road. No romance for Jorah!
Upon getting confirmation of Theon's capture and torture on the HBO series, his sister Yara runs off to save him with her fastest ship. In the books, his sister, who is called Asha (changed on the show so as not to be confused with Osha), does not do this right away, or for love. For her, rescuing Theon — which she plans to do by land instead of sea — is a strategy that will help her take control of the Iron Islands, whose leadership is in dispute with the arrival of their uncles Euron and Victarion, one or both of whom presumably will be seen in season four. Still, it's nice to see that she cares.
After his capture at Winterfell, Theon is presumed dead until a piece of his skin turns up at the Red Wedding, courtesy of the Boltons. Theon's torture and mutilation at the hands of Ramsay Snow happens almost entirely offstage and is only suggested until he reappears in book five, at that point so beaten down and disfigured that no one recognizes him, especially since he is now going by the name Reek. His poor flayed finger had become infected, which is why he begged Ramsay to just cut it off, among other parts (although the castration is implied, not confirmed). In the show, we're seeing the beginnings of the torture and his psychological breakdown, and we're coming to understand why he might begin to call himself Reek, a name that has been used before in the books by other people (including Ramsay). Reek is not a person, but an identity, and Theon becoming Reek is just one step in the dastardly plan the Boltons have for him.