With its multiple timelines and complicated alliances, Netflix's The Witcher isn't afraid to throw audiences in the deep end of its fantasy world.
But even after acclimating to monsters like kikimora, or epochal magical events like the Confluence of the Spheres or the Curse of the Black Sun, The Witcher still has plenty of surprises, including a literal one: the strange custom known as the "Law of Surprise."
Introduced in the fourth episode of Netflix's The Witcher, "Of Banquets, Bastards and Burials," the Law of Surprise might seem at first like a relatively unimportant custom, but the consequences of its invocation reshape the history of The Witcher world. It's therefore absolutely essential to understand just what is the Law of Surprise and what it means for the titular witcher.
In the episode, Geralt of Rivia (The Witcher's witcher) is a guest at a banquet hosted by Queen Calanthe (Jodhi May), who hopes to forge a political alliance by marrying away her daughter, Princess Pavetta (Gaia Mondadori). But her machinations are upended when a knight "of no renown, from a backwater hamlet," barges into the banquet hall and demands an audience with the queen.
"I am Lord Urcheon of Erlenwald, and I have come to claim your daughter's hand in marriage," the knight says, shortly before its revealed he's been cursed with the face of a hedgehog. "I come to claim what is rightfully mine: Pavetta, by the Law of Surprise."
The Law of Surprise is an ironclad custom in the world of Andrzej Sapkowski's The Witcher novels, which is often invoked after someone has saved the life of another. It is a boon granted to the savior; a debt that can be characterized in two ways, gifting the savior "the first thing that comes to greet you" or "what you find at home yet don't expect." Based in Slavic mythology (like much of The Witcher), the Law of Surprise comes up repeatedly throughout the novel series, including in The Last Wish and Sword of Destiny.
Calanthe ignores Lord Urcheon's claim, instead setting her guards upon him. But the honor-bound witcher Geralt sides with the cursed knight, fighting the queen's men to a standstill. The hedgehog explains the basis for his claim: he once saved Calanthe's late husband, King Roegner, from "a certain death."

"By tradition, I chose the Law of Surprise as payment. Whatever windfall he came home to find would be mine," Lord Urcheon said, partially explaining the custom.
Others in the banquet hall push back against Calanthe's fury, including Eist of Skellige (Björn Hlynur Haraldsson), who we already know from the first episode of The Witcher will one day marry the queen.
"Asking for payment with the Law of Surprise is as old as mankind itself," Eist tells Calanthe. "It's an honest gamble. As likely to be rewarded with a bumper crop as a newborn pup. Or, a child of surprise."
"A promise made must be honored, as true for a commoner as it is for a queen," Geralt tells Calanthe before she finally relents. But Lord Urcheon's invocation of the Law of Surprise is just the beginning, setting the stage for an invocation of the custom that will forever change the future of The Witcher.
Mere moments after Calanthe accepts her daughter Pavetta's marriage to the hedgehog knight, Lord Urcheon offers a boon of his own to Geralt. The witcher says he wants nothing, but Lord Urcheon insists, saying, "I cannot start a new life in the shadow of a life debt."

Geralt relents and casually invokes the Law of Surprise for himself, unthinking of the potential consequences. "Give me that which you already have, but do not know."
Calanthe is immediately horrified, because she knows what Urcheon does not: Pavetta is pregnant with the magically powerful child Ciri (Freya Allan).
The scene in "Of Banquets, Bastards and Burials" involving the Law of Surprise helps explain why Calanthe sends Ciri to find Geralt of Rivia in the very first episode of The Witcher (which is partially set far in the future of the fourth episode's banquet): Ciri and Geralt are bound together by both destiny and custom.