A Darker Shade of Magic recap

Four Londons occupy the same point in different worlds: Grey London has forgotten magic, Red London thrives on it, White London starves for it, and Black London was consumed by it and sealed away. Only Antari, marked by one solid black eye, can travel between them. Kell, one of two living Antari, serves the Red London crown as its messenger and smuggles trinkets on the side. Handed a black stone that turns out to be a fragment of Black London's magic, he is hunted for it, robbed of it in Grey London by a thief named Delilah Bard, and forced into an alliance with her to carry it back where it came from. The stone grants what its holder asks and takes something in return, and the rulers of White London want it. Kell and Lila fight their way through White London, but Astrid Dane reaches Red London first and takes Prince Rhy's body. Kell kills her, binds his own life to Rhy's to save him, and sends the stone into Black London inside the dying Holland before sealing the door. Lila leaves for a ship of her own.

Four Londons sit stacked on the same spot in different worlds. Grey London has forgotten that magic exists; Red London is rich with it; White London is a hard, cold place where a dying magic must be taken by force; and Black London was consumed by magic and sealed off long ago, so completely that its name is barely spoken. Only Antari, blood magicians marked by a single solid black eye, can pass between them. Kell is one of two living Antari. He was brought into the Red London palace as a small child and raised beside Prince Rhy, and he serves the Maresh crown as its official messenger, carrying letters between the rulers of the three worlds still open. He also breaks the law he is meant to uphold, smuggling small objects across the boundaries for collectors who can never travel themselves. In Grey London, meanwhile, a thief named Delilah Bard robs a carriage at knifepoint. She has grown up on the street, dresses as a boy, and wants a ship of her own more than she wants safety.

Kell's rounds take him first to Grey London, where he delivers the crown's letters to an ailing King George, who is the only person in that world who knows what Kell is, and sells a small enchanted stone to Ned Tuttle, an eager young collector. He then crosses to White London, a grey and brutal city ruled by the twins Athos and Astrid Dane, who hold power by fear and keep the world's other Antari, Holland, bound to their service by a spell carved into his skin. Holland tells Kell plainly that the difference between their two lives is luck and nothing else. On his way out of the city, a stranger presses a package on Kell as payment for a delivery. Inside is a black stone marked with an unfamiliar symbol, and the magic in it does not belong to any of the three worlds still standing. It is a piece of Black London, and Kell has just carried it home.

Kell realizes what the stone is and finds that he cannot simply be rid of it: it does what its holder asks and takes something in return, and it does not want to be put down. Word of it moves faster than he does. Attacked in Red London and unable to explain himself to the crown without admitting to years of smuggling, he crosses into Grey London to get the stone out of a living world, and there Delilah Bard picks his pocket and takes it. She has no idea what she has stolen, only that it is worth something, and when she tests it the stone answers her. Kell hunts her down through Grey London while the people who want the stone hunt them both.

Kell finds Lila and, after a short and hostile negotiation, the two of them end up working together: she will not give the stone back and he cannot leave without it. Holland arrives in Grey London under orders to bring the stone to the Danes, and the hunt turns lethal for anyone standing near either of them. Lila, who has spent her life wanting a bigger world, now has proof that there are three more of them, and she refuses to be left behind. She and Kell escape together with the stone, and Kell brings her across into Red London, which no one from her world has any business seeing.

In Red London, Kell and Lila conclude that the stone cannot be destroyed by any magic they have, and that the only place it can safely go is back to Black London, through a door no one has opened in centuries. The stone keeps working on whoever holds it, offering exactly what that person most wants, and the hunt for it has already cost Lila the closest thing she had to a friend in her own world: Barron, the tavern keeper who gave her a room, is dead. Rhy is at the center of the danger without being told why, the crown's guard is closing on Kell, and the Danes are not going to stop. Kell decides to carry the stone to White London himself and end the matter at its source, and Lila, who has no intention of being sent home, goes with him.

White London is worse than Kell described it, and the Danes are ready for them. Kell is taken and held by Athos, who is expert at making a bound person obey, and the stone changes hands. Lila, underestimated because she is a Grey Londoner with no magic to speak of, gets close enough to Athos to put a knife in him and kills him. With Athos dead, Kell is able to break the spell that has held Holland in service for years, though Holland has little left to be grateful with. The victory is incomplete: Astrid is not in her city. She has already crossed into Red London, and she went for the one person Kell would trade anything to protect.

Kell and Lila return to Red London to find that Astrid Dane has taken Prince Rhy's body as her own, intending to trade a dying world for a living one. Kell has no way to drive her out and no way to spare his brother: to kill her he has to kill Rhy. He does it, and then uses Antari blood magic to bind his own life to Rhy's, dragging him back. Rhy lives, but the two of them now share pain and Rhy cannot die while Kell survives, a bond neither the king nor the queen knows about. With Holland mortally wounded, Kell binds the black stone into him and pushes him through the door into Black London, then seals the passage with his own blood, putting the stone beyond anyone's reach at the cost of the man who carried it. Red London keeps its heir and never learns the price. Kell's travelling is now something the crown means to control, and Lila, offered a place in a world full of magic, chooses instead to leave for a ship and a life of her own.

In White London, Lila kills Athos Dane and Kell breaks the binding spell that has held Holland in service, but Astrid has already crossed into Red London and taken Prince Rhy's body for her own. Kell is forced to destroy her, which means killing his brother, and then uses Antari blood magic to tie his own life to Rhy's so that Rhy lives again; from that moment the two of them share pain, and Rhy cannot die while Kell survives. With Holland mortally wounded, Kell binds the black stone into him and pushes him through the door into Black London, then seals the passage with his blood, putting the stone beyond reach at the cost of the man who carried it. Red London survives with its heir restored and its crown unaware of what the rescue actually cost. Kell's bond with Rhy is a secret that binds them both, and his freedom to travel is now something the king intends to control. Lila, offered a place, chooses the sea instead: she leaves for a ship and a life of her own in a world where magic is real. Holland is presumed dead in a world nothing can enter.