In GRRM's original story, it was a trilogy of books. The redacted was where it was supposed to end.
Book 1's premise:
The first threat grows from the emnity between the great houses of Lannister and Stark as it plays out in a cycle of plot, counterplot, ambition, murder, and revenge, with the iron throne of the Seven Kingdoms as the ultimate prize. This will form the backbone of the first volume of the trilogy, A Game of Thrones.
Book 2's premise:
While the lion of Lannister and the direwolf of Stark snarl and scrap, however, a second and greater threat takes shape across the narrow sea, where the Dothraki horselords mass their barbarian hordes for a great invasion of the Seven Kingdoms, led by the fierce and beautiful Daenerys Stormborn, the last of the Targaryen dragonlords. The Dothraki invasion will be the central story of my second volume, A Dance with Dragons.
Book 3's premise:
The greatest danger of all, however, comes from the north, from the icy wastes beyond the Wall, where half-forgotten demons out of legend, the inhuman others, raise cold legions of the undead and the neverborn and prepare to ride down on the winds of winter to extinguish everything that we would call "life." The only thing that stands between the Seven Kingdoms and an endless night is the Wall, and a handful of men in black called the Night's Watch. Their story will be [sic] heart of my third volume, The Winds of Winter. The final battle will also draw together characters and plot threads left from the first two books and resolve all in one huge climax.
"Catelyn Stark will be forced to flee north with her son Bran and her daughter Arya. Hounded by Lannister riders, they will seek refuge at the Wall, but the men of the Night's Watch give up their families when they take the black, and Jon and Benjen will not be able to help, to Jon's anguish. It will lead to a bitter estrangement between Jon and Bran."
Jaime Lannister will follow Joffrey on the throne of the Seven Kingdoms, by the simple expedient of killing everyone ahead of him in the line of succession and blaming his brother Tyrion for the murders. Exiled, Tyrion will change sides, making common cause with the surviving Starks to bring his brother down, and falling helplessly in love with Arya Stark while he's at it. His passion is, alas, unreciprocated, but no less intense for that, and it will lead to a deadly rivalry between Tyrion and Jon Snow.
The Main Characters:
Five central characters will make it through all three volumes, however, growing from children to adults and changing the world and themselves in the process. In a sense, my trilogy is almost a generational saga, telling the life stories of these five characters, three men and two women. The five key players are Tyrion Lannister, Daenerys Targaryen, and three of the children of Winterfell, Arya, Bran, and the bastard Jon Snow. All of them are introduced at some length in the chapters you have to hand..
So Bran, Jon, Tyrion, Arya and Dany were the main characters.
I have quite a clear notion of how the story is going to unfold in the first volume, A Game of Thrones. Things will get a lot worse for the poor Starks before they get better, I'm afraid. Lord Eddard Stark and his wife Catelyn Tully are both doomed, and will perish at the hands of their enemies. Ned will discover what happened to his friend Jon Arryn, before he can act on his knowledge, Robert will have an unfortunate accident, and the throne will go to his sullen and brutal son, Joffrey, who is still a minor. Joffrey will not be sympathetic and Ned Stark will be accused of treason, but before he is taken he will help his wife and his daughter Arya escape back to Winterfell.
Starts out similarly. Cat's with Ned in King's Landing though. Arya and Cat make it back to Winterfell though.
Each of the contending families will learn it has a member of dubious loyalty in its midst. Sansa Stark, wed to Joffrey Baratheon, will bear him a son, the heir to the throne, and when the crunch comes she will choose her husband and child over her parents and siblings, a choice she will later bitterly rue. Tyrion Lannister, meanwhile, will befriend both Sansa and her sister Arya, while growing more and more disenchanted with his own family.
Sansa marries Joffrey and has his son. So that's a big change. Tyrion befriends Sansa (sorta happens) and Arya.
Young Bran will come out of his coma, after a strange prophetic dream, only to discover that he will never walk again. He will turn to magic, at first in the hope of restoring his legs, but later for its own sake. When his father Eddard Stark is executed, Bran will see the shape of doom descending on all of them, but nothing he can say will stop his brother Robb from calling the banners in rebellion. All the north will be inflamed by war. Robb will win several splendid victories, and maim Joffrey Baratheon on the battlefield, but in the end he will not be able to stand against Jaime and Tyrion Lannister and their allies. Robb Stark will die in battle, and Tyrion Lannister will besiege and burn Winterfell.
Tyrion burns Winterfell. Joffrey is maimed on the battlefield by Robb Stark. He loses to Tyrion and Jaime though. No Tywin in the story.
Jon Snow, the bastard, will remain in the far north. He will mature into a ranger of great daring, and ultimately will succeed his uncle as the commander of the Night's Watch. When Winterfell burns, Catelyn Stark will be forced to flee north with her son Bran and her daughter Arya. Wounded by Lannister riders, they will seek refuge at the Wall, but the men of the Night's Watch give up their families when they take the black, and Jon and Benjen will not be able to help, to Jon's anguish. It will lead to a bitter estrangement between Jon and Bran. Arya will be more forgiving ... until she realizes, with terror, that she has fallen in love with Jon, who is not only her half-brother but a man of the Night's Watch, sworn to celibacy. Their passion will continue to torment Jon and Arya throughout the trilogy, until the secret of Jon's true parentage is finally revealed in the last book.
Big changes: Jon falls in love with Arya and Arya falls in love with Jon. Bran and Jon become enemies after Jon refuses to help the Starks leading to Cat's death. Jon's parentage reveal solves the love problems between Arya and Jon.
Abandoned by the Night's Watch, Catelyn and her children will find their only hope of safety lies even further north, beyond the Wall, where they fall into the hands of Mance Rayder, the King-beyond-the-Wall, and get a dreadful glimpse of the inhuman others as they attack the wilding encampment. Bran's magic, Arya's sword Needle, and the savagery of their direwolves will help them survive, but their mother Catelyn will die at the hands of the others.
Cat is killed by the Others. Arya journeys north with Bran and Cat. Arya is replaced by Meera Reed in the actual story.
Over across the narrow sea, Daenerys Targaryen will discover that her new husband, the Dothraki Khal Drogo, has little interest in invading the Seven Kingdoms, much to her brother's frustration. When Viserys presses his claims past the point of tact or wisdom, Khal Drogo will finally grow annoyed and kill him out of hand, eliminating the Targaryen pretender and leaving Daenerys as the last of her line. Danerys [sic] will bide her time, but she will not forget. When the moment is right, she will kill her husband to avenge her brother, and then flee with a trusted friend into the wilderness beyond Vaes Dothrak. There, hunted by [unclear] of her life, she stumbles on a [something about dragon eggs] a young dragon will give Daenerys [unclear] bend [unclear] to her will. Then she begins to plan for her invasion of the Seven Kingdoms.
Daenerys and Viserys have a good relationship and she kills Drogo for kill her brother. She just randomly finds dragon eggs though.
Tyrion Lannister will continue to travel, to plot, and to play the game of thrones, finally removing his nephew Joffrey in disgust at the boy king's brutality. Jaime Lannister will follow Joffrey on the throne of the Seven Kingdoms, by the simple expedient of killing everyone ahead of him in the line of succession and blaming his brother Tyrion for the murders. Exiled, Tyrion will change sides, making common cause with the surviving Starks to bring his brother down, and falling helplessly in love with Arya Stark while he's at it. His passion is, alas, unreciprocated, but no less intense for that, and it will lead to a deadly rivalry between Tyrion and Jon Snow.
Jaime Lannister kills Joffrey and everyone in front of him in the line of succession. Jaime becomes king. Tyrion switches sides to the Starks. Tyrion falls in love with Arya and just like Bran becomes enemies with Jon Snow.
The redacted part that says how the first book would've ended:
Brandon Stark becomes King likely with Tyrion's help.
They are Jon's enemies to the south.
Daenerys Targaryen invades Westeros. The Others invade south. Jon is at the Wall or King in the North.
So Robert dies-> Joffrey becomes King-> Jaime kills Joffrey and becoms king-> Bran and Tyrion knock Jaime off the throne and Brandon Stark becomes king
That was where book 1 ends.
mod edit: additional context
It's pieced together from a partially redacted letter to his agent about a planned trilogy (lol) of books that would eventually become ASoIaF from 1993 IIRC.
