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->''No one else will remember or know what we are going to say here. Even I will forget, unless you let me remember. This is the way things work here. No one has to be a stranger.''

''The Quantum Thief'' is Hannu Rajaniemi's debut sci-fi novel, and the first of a trilogy.

In a post-[[TheSingularity Singularity]] solar system slowly being eaten by a community of uploaded minds, Mars has remained independent and unique thanks to its extreme attitude to privacy: all memory is externally stored and encrypted, and you can't access a memory unless everyone involved consents. This makes life pretty difficult for detective Isidore Beautrelet, but as a native Martian he wouldn't have it any other way.

Also due to make life difficult for Isidore is the GentlemanThief Jean le Flambeur, a figure of legend who's modeled himself on Literature/ArseneLupin. A debt of honor requires Jean to commit a daring heist, but first he must steal back his own memories from the Oubliette of Mars. He's accompanied by Mieli, the bitter transhuman masterminding the mission, her flirtatious spaceship, and the goddess she reluctantly serves.

The second part of the trilogy, ''The Fractal Prince'', came out in late 2012. The third and final installment, ''The Causal Angel'', came out in July 2014.

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!!''The Quantum Thief'' provides examples of:
* AIIsACrapshoot: The Sobornost gave up on trying to create intelligence without sapience or make minds not based on the human cognitive architecture after they ended up creating the mindless, destructive insanity that was [[EldritchAbomination the Dragons]], which are now used only as terror weapons. Disturbingly, this means that every single system that the Sobornost uses is powered by a spliced, copy-pasted and mutilated version of an uploaded human mind.
* TheAlternet: The Spimescape is the closest equivalent of a Solar System-wide information network, though it's heavily divided and fragmented.
* BarbarianTribe: The Oortians are seen like this by the rest of the Solar System. They live in hollowed out comets in small family groups and construct handcrafted spaceships, AIs and other fantastic creations out of smartcoral through religious rites.
* BewareTheNiceOnes:
** The hsien-kus are eccentric scholars, generally considered the silly aunts of the Sobornost family. They devote themselves wholly to preserving as much of the past world in their virtual constructs as they can. [[spoiler:And they are building a system that would tear Earth apart molecule by molecule to be uploaded in perfect accuracy to their ''guberniya'' forever.]]
** The Zokus are generally considered the "good guys" compared to the Sobornost, as they respect individual choice and freedom, but they ''will'' MindRape you if you get on their wrong side or have something that they really want. In the latter case they're just really apologetic about it. In the former, they get ''creative''.
* BiggerOnTheInside: Most spaceships in this universe tend to be quite small, sometimes small enough to fit in a pocket, but those made by Sobornost or the Zoku have virtual spaces that are only limited by their owners' imaginations.
* BilingualBonus[=/=]MeaningfulName: The Oortians speak the author's native tongue, Finnish. Mieli means "mind" and Sydän means "heart". Perhonen stands for "butterfly".
** Not strictly a Bilingual Bonus, but [[spoiler:knowing that 'oubliette' is a word for a type of dungeon does make a reveal at the end less surprising.]]
** Zoku means "community" in Japanese.
** Jean le Flambeur's Oubliette alter ego is named Paul Sernine -- an anagram of ArseneLupin, on whom Jean's character is based.
*** We later learn that Jean is a longtime fan of the Lupin stories, which implies that the choice of name was intentional in-universe, on Jean's part.
* {{Bizarrchitecture}}: The city of Oubliette on terraformed Mars is built on the backs of titanic Atlas Quiets, uploaded human minds controlling gigantic robots. In result it's always on the move, and its layout is constantly changing as the Quiets move around each other. As far as bizzareness of architecture goes, it's actually one of the more ''normal'' locations in the novel's transhuman future.
* BlueAndOrangeMorality: The Sobornost see it as their duty to preserve every mind in existence, but hold all matter in disdain and have no kind of respect to the concept of free will. The Zoku on the other hand don't believe in any kind of permanence, and cheerfully alter their own identities to suit their latest game. They also loathe the concept of devoting oneself to any kind of ideal, considering anyone who is controlled by an ideology living dead.
* BoxedCrook: After getting broken out of the Dilemma Prison, Jean is put in a Sobornost body that's functions can be limited or cut off by Mieli at any time to ensure his compliance.
* BrokenBird: Mieli. She devoutly serves the Sobornost Founder Pellegrini to [[spoiler:to get the uploaded mind of her beloved Sydän back to her. ]]
* ClockPunk: The Oubliette, most notably with the Watches that measure each citizen's time as a Noble before they are turned into robotic Quiet.
** Also used, though not described in very great detail, in the wildcode desert surrounding the city of Sirr on Earth, as complicated electronics and nanotech get destroyed in a flash by the native nanotechnology.
* CoolShip: Mieli's ''Perhonen'' and Jean's old ship, ''Leblanc'', definitely qualify.
* EldritchAbomination: The Dragons and the All-Defector are (post)human creations, but they are alien and terrifying enough to qualify.
* EmperorScientist: Most of the seven Sobornost Founders were originally some of the world's most brilliant scientists from the early era of mind-uploading in the 2060's, and continue their experiments in increasingly massive scale to the present day. Notably, they work in very different fields of expertise; the hsien-kus are sociologists and historians while the chens focus on physics, for example. [[spoiler: The King of Mars also qualifies.]]
* ExactlyWhatItSaysOnTheTin: The All-Defector always defects, no exception.
* ExpendableClone: The Sobornost Founders have uploaded their minds to millions of artificial bodies. These collectives are called copyclans, and their members synchronize their memories and brainpower whenever they are together, allowing them to be everywhere in their massive empire at once. It doesn't matter if a few die, since there's always backups. Although their interests don't always coincide, and some of the Founders are said to be in war against themselves. Also, the main protagonist, Jean le Flambeur has millions of copies of himself trapped forever in the Dilemma Prison, but he's just happy that he was the one that got away.
** The narration refers to the Sobornost Founder copyclans with a lower-case initial to emphasize their expendable nature: the hsien-kus, the sumangurus, the chens, the pellegrinis, etc.
* FantasticSlurs: The Zoku refer to the Sobornost and anyone else who devotes their life to an abstract ideal as "meme zombies", while the Sobornost call the Zoku and anyone else opposing their plan to remove uncertainity from the universe as "quantum filth".
* FantasyCounterpartCulture: The Oortians are descendents of Finns, while the Zoku date their history to [[spoiler:the Internet subcultures of the 21st century.]]
* ForeignCussWord: Mieli swears like a sailor at times -- in Finnish.
* GentlemanThief: The title character.
* GodEmperor: The Sobornost Founders have programmed every uploaded mind in their collective to feel religious awe towards them -- including their own later generation copies.
* GoodSmokingEvilSmoking: The pellegrinis almost always appear to be smoking cigarettes when they make an appearance.
** Sumanguru smoked cigars when he was human, but unlike Pellegrini, his avatars don't follow the habit.
* HumanoidAbomination: The Sobornost Founders arguably qualify. The All Defector has only been seen as a humanoid so far, but then [[NothingIsScarier it's exact nature isn't clear]]
* ImpossibleThief: pretty much any time Jean le Flambeur pulls of a serious con he qualifies for this. Most spectacularly, in the closing moments of the second book [[spoiler:it turns out the artifact everybody is fighting over is a fake, and he had already stolen the real one from them without leaving a single trace]]
* InfoDrop: The author seems particularly averse to exposition, so the only hope a reader has to figure anything out is to piece all the disparate tidbits together. [[LoveItOrHateIt Depending on your disposition]], this is either part of the series' charm, or horribly frustrating.
* MemoryGambit: [[spoiler:Jean]] pulls this surprisingly often, with mixed results. The biggest is unveiled in ''The Causal Angel'', wherein we learn that [[spoiler:an earlier, more ruthless Jean le Flambeur arranged to be incarcerated in the dilemma prison after a memory wipe, hoping he could escape as a better person to activate a powerful device that [[OnlyThePureOfHeart can only be used by those with good intentions]]. Of course, [[AmnesiacDissonance the new, nicer Jean is horrified]], and [[NiceJobFixingItVillain promptly rebels against his former self.]]]]
* NiceJobBreakingItHero: In ''The Causal Angel'', [[spoiler:Jean crashes the Zoku's quantum communication network as a distraction in order to rescue Mieli. Unfortunately, in doing so, he cripples the Zoku moments before they're attacked by a force of Sobornost ships controlled by the All-Defector.]] Oops.
* NotAGame: Isidore's detective work, as he tells Pixel.
* OrderVsChaos: The Sobornost see their entire existence as embodiment of Order, imposing themselves on the chaotic universe to eliminate death and uncertainity, but in particular their Protocol War against the Zoku was motivated with this ideology, since the Zoku base their technology on the unpredictable quantum states of matter and reject the concept of permanent identity.
* ProudWarriorRaceGuy:
** Pixil's Zoku. What would you expect from an upload collective descended from online roleplaying guilds?
** The Sumanguru Warminds of the Sobornost Collective, based on an African warlord adopted in the Founders' ranks, is a more grim version of the trope.
* PracticalCurrency: The currency on Mars is ''time''. When one's time as a Noble runs out, their mind gets put into a Quiet work body for a few years to earn more. Think [[XMeetsY community service meets forced labor]].
* SapientShip[=/=]SpaceshipGirl: Perhonen.
* ScaryBlackMan: The sumangurus when they lower themselves to wearing flesh.
* ShoutOut: Countless, both obscure and popular.
** ''Causal Angel'' briefly features Notch-zoku that is devoted to building monuments and whose symbol is a [[MineCraft crudely carved man with a pickaxe]].
** And [[CthulhuMythos Mythos-zoku]]. And [[NeonGenesisEvangelion Evangelion Zoku]]. The Zoku are one big collection of Internet-culture Shout Outs because many of them are supposed to be the very same people who contribute in those today and feel nostalgic about them.
* TheSingularity:
** The breakthrough that lead to the discovery of mind uploading happened approximately 300 years before the story, and the development of technology went out of control in the matter of years, culminating in the event known as the Collapse, which rendered Earth nearly uninhabitable.
** Another Singularity-event known as the Spike, which lead to the total destruction of the planet Jupiter, happened only some years before the story, and is a driving force in the background of the plot, as all parties are attempting to find out exactly what happened.
* SocialEngineering: Like all good conmen, Jean plays his opponents and innocent bystanders like a fiddle to reach his desired goals.
** The Great Game Zoku prefer to gather information through this rather than MindRape, if they have the time. They can build immensely elaborate scenarios for the person they want to probe and determine what they know from their choices and actions inside the simulation.
* SpannerInTheWorks: Jean is a spanner to just about every plotter in the Solar System, eventually including himself, thanks to his past MemoryGambit -- he failed to take into account that by allowing his personality to be modified to accomplish his greatest achievement he might no longer be willing to follow the steps of his XanatosRoulette exactly as he originally planned.
* SteamPunk: Some Zokus are fond of the aesthetic. At one point in ''Causal Angel'' Jean has to remind himself that the man he is trying to con is not a goofy steampunk cyborg, but a posthuman entity with a quantum brain pretending to be one for his own amusement.
* StickyFingers: Jean will risk going to a literal hell just to steal a piece of jewelry.
* TooDumbToLive: The pellegrini honestly thought that she could use the All-Defector for her own ends, forgetting what defines that entity. It's in the name!
* {{Transhuman}}: Practically every character in the story, to greater or lesser extent.
* ViewersAreGeniuses: The book introduces numerous exotic concepts by simply referring to them by name, and expects the reader to deduce from the context what they mean. Even when a concept ''is'' described, it's rarely done in great detail, or more than once. A great deal of the author's astronomical expertise is also poured into the story, using for the moment hypothetical laws of physics as basis for several [[MagicFromTechnology Sufficiently Advanced]] technological innovations, such as strangelet bombs.
* YouWillBeAssimilated:
** If the Sobornost has their way, all minds will be uploaded as Gogols into their planet-sized ''gubernya'' diamonoid brains. It seems that they will ask a permission from [[{{Transhuman}} Transhumans]] first, at least if they're not hostile. Baseline humans don't get a say in the matter.
** The All-Defector's ultimate goal is nothing less than to ''become'' the entire universe.