A cruel boy king choked to death in his mother's arms at his own wedding feast, and an innocent was seized to hang for it. The poison, the plotters the pages name, and the ruin it worked on the house that ordered the Red Wedding.
What the realm knows
The realm remembers the Purple Wedding chiefly for how the groom died: choking, clawing at his own throat, his face gone the colour that gave the day its name, dead in his mother's arms before the last course was cleared. King Joffrey Baratheon — cruel boy, dubious son of a dead king — wed Margaery Tyrell in a lavish feast at King's Landing, and did not live to consummate the marriage. That much any teller of tales can give you, and the screen gave it plainly.
What the realm knows, then, is a poisoning and a scapegoat: the king struck down at his own wedding, and his uncle, the dwarf Tyrion Lannister, seized and accused of the deed. What the realm did not know for a long while — what the chronicle can now set down, drawn from the pages — is that the true hands behind the strangler's work were not the hands that were bound for it. The particulars below are book substance, and are veiled accordingly.
The full account
The wedding of the boy king
It was to be the marriage that sealed the crown's victory: the Lannister king wed to the flower of Highgarden, whose swords and stores had turned the war. No expense was spared. Seven-and-seventy dishes were served in the throne room, a monstrous pigeon pie was cut with the king's own sword, and mummer dwarfs were made to ride about mocking the fallen kings of the late war, that the court might laugh at the dead. Through it all Joffrey played the boy he was, small and spiteful, saving his sharpest cruelties for his uncle Tyrion, whom he humiliated before the hall.
The king took wine and pigeon pie, and began to cough. The cough became a choking, the choking a seizing; he tore at his throat as though to open it, his skin darkening, his eyes weeping blood. His mother the queen screamed for a maester and cradled him as he died. Before he was cold she had already found the meaning of it, and pointed: her brother Tyrion had poured the wine, and Tyrion, whom she had hated all his life, would answer for the king.
The strangler
The poison that killed Joffrey is a rare and cruel one the maesters call the strangler, a thing crystallised from the leaves of a plant of the eastern isles, which seizes the muscles of the throat and closes it against all air. Steeped, the crystals resemble nothing so much as coarse sugar or a scatter of gemstones, and there lay the cunning of the plot — for the means of the murder was worn openly, in plain sight, all through the feast.
Sansa Stark, the dead Robb's sister and Tyrion's unwilling wife, had been given a hairnet strung with black amethysts, and one of those stones was no stone at all. In the press of the wedding a stone went missing from her hair, and the strangler found its way into the king's cup. The reader who traces the crystals back through the pages will find that Sansa was made the unknowing vessel, and that the removal of a single amethyst was the whole murder in miniature — done in a crowded hall, before a thousand eyes, by hands the crowd never marked.
The conspirators, named
The pages let the truth out slowly, but they let it out. The murder had two chief architects working to one another's profit. The first was Petyr Baelish, called Littlefinger, who had furnished the poisoned hairnet and who wanted Sansa Stark spirited out of the capital in the chaos a royal death would make — a claim to the north being a useful thing for a man of small birth and large ambition to hold. The second was Olenna Tyrell, the Queen of Thorns, grandmother to the bride.
The old woman's motive was plainer than the mockingbird's: she had heard enough of Joffrey's cruelty to know what manner of husband her granddaughter was being sold to, and she preferred Margaery a widowed queen to a tormented wife. Between them they arranged that a monster should die and an innocent should hang for it, and both very nearly had their wish. A maester notes the shape of it without admiration: the boy the whole realm had cause to kill was killed at last by the two people at the feast with the coolest heads and the least love for him.
The scapegoat
Sansa Stark vanished from the wedding in the confusion, taken to safety by Littlefinger's design, and so the crown's grief needed another target. It found Tyrion. Hated by his sister, mistrusted by his father, and conveniently at hand with wine on his hands, the Imp was seized and charged with kingslaying and kinslaying both, and made to stand a trial that had decided its verdict before it opened.
That trial, and the ruin it worked upon House Lannister, the chronicle treats as its own matter — how a son cornered by his own blood answered his father at the last, and what that answer cost the Old Lion. Here it is enough to mark that Joffrey's death, plotted to save one girl and one bride, tore a second wound through the family that had ordered the Red Wedding, and that the poisoned cup at the Purple Wedding did more to unmake the Lannisters than any of Stannis's swords. Readers may follow the thread onward to the trial of the Imp in the timeline.
Joffrey's little brother Tommen, a gentler and more biddable child, was crowned in his place, and Margaery Tyrell — widowed but not undone — was in time betrothed to the new boy king, so that Highgarden kept its grip upon the crown through a second marriage. The peace the wedding was meant to seal was seized after all, though over a fresh corpse. Of the smallfolk who had suffered the boy's reign, few wept; a king who is loved is mourned in the streets, and Joffrey's passing raised more quiet relief than grief.
The lasting wound was struck within House Lannister itself. Tyrion's trial fractured the family beyond mending and set in motion the fall of Tywin, so that the murder plotted by an old woman and a small-born schemer cost the greatest house in the realm its head and its future. Littlefinger carried Sansa away to the Vale to play a longer game, and Cersei Lannister, robbed of the son she loved and left with the ones she could not master, began the slow unravelling that the later pages record.
The Purple Wedding is the name readers gave the marriage feast of King Joffrey Baratheon and Margaery Tyrell at King's Landing, at which Joffrey was poisoned and died choking, his face gone purple. His uncle Tyrion Lannister, who had poured his wine, was seized and accused of the murder.
How was Joffrey poisoned?
With a rare poison the maesters call the strangler, which seizes the throat closed. Crystallised, it looks like coarse sugar or a dark gemstone, and it was hidden in plain sight among the black amethysts of Sansa Stark's hairnet. A stone went missing during the feast, and the poison found its way into the king's cup.
Who really killed Joffrey?
The pages reveal two architects: Petyr Baelish, called Littlefinger, who supplied the poisoned hairnet and wanted Sansa spirited away in the chaos, and Olenna Tyrell, the Queen of Thorns, who would rather see her granddaughter a widowed queen than wed to a monster. Tyrion, the accused, was innocent.
What did Joffrey's death lead to?
Tyrion was tried for the murder, and that trial fractured House Lannister and set in motion the fall of Tywin — arguably doing the family more harm than any battle. Joffrey's gentler brother Tommen was crowned, and Margaery was in time betrothed to him, keeping Highgarden's grip on the throne.