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Set initially in the same universe as ''Literature/TheMoonIsAHarshMistress'', ''The Cat Who Walks Through Walls'' is one of Creator/RobertAHeinlein's later works. It features yet another soldier-of-fortune in the character of Richard Ames, a retired colonel who begins the story living on a cushy space station. His easy life is quickly upended when he marries Gwen Novak, who is secretly a Time Agent, and on a mission to save the universe. Richard and Gwen are chased across the galaxy by unknown enemies, and eventually take refuge in a multiverse paradise, populated by many familiar characters from other Heinlein books, including [[Literature/StrangerInAStrangeLand Jubal Harshaw]] and the ubiquitous [[AuthorAvatar Lazarus Long]], the latter of whom tries to recruit Richard into his TimePolice. Lazarus' ultimate goal is to rescue Mycroft Holmes, a dormant supercomputer with the power to perfectly predict the consequences of time manipulations.

The story operates heavily on the ideas perpetuated in ''Literature/TimeEnoughForLove'' and ''Literature/TheNumberOfTheBeast'' -- TheWorldAsMyth, Heinlein's personal philosophies regarding group marriages and the perils of socialism. It also features one of the most confusing endings of any of Heinlein's novels, leaving two characters stranded and alone and refusing to say whether or not anything was actually achieved. In fact, the resolution to the {{Cliffhanger}} ending is not revealed until the sequel, ''Literature/ToSailBeyondTheSunset''.

Despite the title, this is definitely ''not'' a part of ''Literature/TheCatWhoSeries''.

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!!This novel provides examples of:

* AchievementsInIgnorance: Pixel, the titular cat, can walk through walls and possibly through space-time-universe. At a loss to explain how, the characters theorize that he doesn't realize that he can't.
* ActionGirl: Despite Richard's attempts at machismo, Gwen is a far superior combatant.
* AlmightyMom: "Auntie" Washington, who springs Richard and Gwen from Hong Kong Luna through sheer force of personality.
* ApocalypticLog: The story is written in first person and framed as Richard writing his memoirs. The final {{Cliffhanger}} is written as a recovered journal recording, without revealing to the reader whether [[spoiler:Richard survives or not]].
* AuthorFilibuster: Heinlein is (in)famous for this. This book is not quite as bad as others, but there are a few notable instances, particularly when the main character is shouting or sneering at bureaucracy.
* AuthorAppeal: All of Heinlein's favorites make an appearance--group marriages, free love, TAANSTAFL, witty (and somewhat sexist) innuendo. This book practically runs on AuthorAppeal.
* BavarianFireDrill: Gwen's misdirection of a customs agent starts with claiming she has a baby alligator in her purse and ends with the two exchanging recipes.
* BolivianArmyEnding: Richard and Gwen are [[spoiler:stranded and apparently left for dead, wounded and nearly out of ammo, and expecting the return of their enemies at any second]].
* CanonWelding: An integral part of The World as Myth concept, this novel brings together heroes from every other timeline Heinlein wrote in the effort to rescue Mycroft Holmes from Luna.
* CasualInterstellarTravel: The World As Myth has been taken to its logical conclusion in this novel, with the Burroughs device enabling instantaneous travel from any point in space-time-universe to any other, and thereby making war possible on a scale never seen before.
* CatsAreMagic: Pixel -- see AchievementsInIgnorance and ChekhovsGunman.
* ChekhovsGunman: Pixel, the titular cat. He walks not only through walls but also space-time-universe, apparently via [[AchievementsInIgnorance not being aware that he can't]]. [[spoiler:In the climax, he alerts the heroes to an ambush by showing up at an opportune moment.]]
* TheChessmaster: Lazarus, and Gwen by proxy. Their scheme to manipulate Richard is epic in its scope, and that itself is only a small part of the larger plan which is to rescue Mike Mycroft from Luna.
* {{Cliffhanger}}: The novel ''ends'' on one. ''Literature/ToSailBeyondTheSunset'' reveals that [[spoiler:everyone survived]].
* CosmicRetcon: By way of persuading Richard to join his organization, Lazarus arranges for a [[NoPartyLikeADonnerParty particular unsavory incident]] from Richard's past to have never happened. This is of course to demonstrate the power of the Burroughs device to literally rewrite histories on a whim.
* CoversAlwaysLie: Richard [[RaceLift is black]].
* DividedStatesOfAmerica: Although not discussed in any great detail, this novel is in the same timeline as ''Literature/{{Friday}}'', where this occurred.
* EasyAmnesia: Tertius medicine seldom employs anesthetic drugs; instead they engage a field that interrupts storage of short term memories. You can be awake and alert while things are done to you, but won't remember it afterward.
* EatTheDog: When passing through Lunar customs, Gwen claims to keep a baby alligator in her purse and declares it to the agent as a pet and possibly food. She is lying, of course; what she really wants is to avoid having the purse searched.
* EveryManHasHisPrice: Richard and Gwen bribe their way through Luna, where this seems to be standard operating practice. Richard himself appears incorruptible but succumbs to a more indirect form of bribery: having his past rewritten.
* ExtrudedBookProduct: Richard claims to write pulp romance novels of no literary merit purely to [[MoneyDearBoy pay his bills]]. He says he tried writing war novels, but his personal experience made it impossible for him to write stories that readers would accept due to RealityIsUnrealistic.
* FreeLoveFuture: On some planets, and most especially Tertius. Richard, who comes from relatively free Luna, is shocked by the level of perceived promiscuity on Tertius, but being a Heinlein character, he quickly adapts.
* GeniusBreedingAct: The Burroughs from ''Literature/TheNumberOfTheBeast'' have by this point in their continuity had a number of children among themselves and with Libby Andy Long, all of whom are indeed supergeniuses.
* GenreBlind / GenreSavvy: Richard is both, simultaneously. He names the real killer--and outlines exactly how it was accomplished--early on in the book, while dismissing that as the kind of [[TakeThatMe lazy plot he would use in one of his his own novels]].
* HandicappedBadass: Richard walks with a cane thanks to an artificial foot -- the original was lost in war. On Tertius, he gets a clone graft replacement.
* HaveWeMetYet: Due to the sheer quantity of overlapping time sequences in the novel, "Are we inverted?" becomes something of a RunningGag.
* HitlersTimeTravelExemptionAct: {{Discussed|Trope}} and {{Deconstructed|Trope}} -- Lazarus' team attempted to assassinate Hitler a few times, but every attempt made things worse in ForWantOfANail fashion. One such timeline ended in nuclear Armageddon and another resulted in the U.S. becoming a fundamentalist theocracy.
* IKnowYouKnowIKnow: Lazarus and his enemies at times seem to be playing this sort of game, in a Sherlock and Moriarty fashion, over who can be more successful at making their manipulations stick. At one point, an entire planet is [[EarthShatteringKaboom nova bombed]] by their adversaries, after which his team of genius mathematicians figures out a scheme to rescue all its people just prior to the event, so that the attack appeared to be successful but nobody was actually lost.
* {{It Is Pronounced Tro-PAY}}: A rather involved discussion takes place regarding the cultural ramifications of the spelling and pronunciation of the name Tolliver/Talliafero. It turns out to be a RedHerring anyway.
* KindheartedCatLover: All of the protagonists are this, another Heinlein trademark.
* KinkySpanking: Young Gretchen offers to let Richard spank her as a blatant sexual proposal. He turns her down, telling her to grow up first. Thanks to TimeTravel, she does, and reinstates the offer. Richard also repeatedly threatens to do this to Gwen, but we never see him carry it out.
* LeftHanging: Some of the characters at the end. This is in part to expand on the concept of characters being written by an eternal and possibly ambivalent Author.
** Subverted in that [[spoiler:Gretchen is pregnant with Richard's child and he hasn't had sex with her... ''yet.'' So we know he survives.]]
* LimbSensationFascination: Richard gets a replacement for the foot he lost in the war. The first thing he does is faint. The second is spend a day reliving the marvel of having two fully functional feet.
* LoveInterest: Gwen gets Richard to marry her in the first chapter, invoking this trope as a means of ensuring that he'll have a reason to do what she wants, while making him think it's all his idea.
* LukeIAmYourFather: The typical formula is varied here by having the son be told by a third party after [[spoiler:figuring out that his donated cloned-tissue foot belongs to Lazarus (because Lazarus is walking around barefoot, like everyone else). Lazarus being his father (thanks to TimeTravel) is why Richard's body didn't reject the foot from Lazarus's clone.]]
* MassiveMultiplayerCrossover: Courtesy of World as Myth, the novel features characters from:
** ''Literature/GloryRoad''
** ''Literature/TheMoonIsAHarshMistress''
** ''Literature/TheNumberOfTheBeast''
** ''Literature/StrangerInAStrangeLand''
** ''Literature/TimeEnoughForLove''
** ''The Rolling Stones'' and a meta-fictional example (Gwen is Hazel from this story and ''The Moon is a Harsh Mistress'') in a character from Gwen's television serial.
* MonowheelMayhem: Richard and Gwen are attacked on the Moon by a heavily armed monowheel. It looks anachronistic because it is; it's one of the rival time factions trying to kill him.
* MostWritersAreWriters: Richard is a writer. He views it as an obnoxious habit, much like smoking, and warns Gwen when she proposes to him that she'll have to deal with him when he gets the itch.
* NoPartyLikeADonnerParty: Richard has a black stain on his soul -- in a particularly desperate moment, his squad was forced into cannibalism to survive. Lazarus arranges to [[CosmicRetcon remove it]].
* ObstructiveBureaucrat: The Manager of the space station where Richard lives evicts him in a passive-aggressive manner by turning off his lights, changing his locks, and refusing to acknowledge that any such was done. Gwen gets even by smearing Limburger cheese on the heating element in the Manager's office.
* OneDegreeOfSeparation: Thanks to multiversal TimeTravel mayhem, it turns out that [[spoiler:Richard is Lazarus' son]], and thus comes by his obstreperousness very naturally.
* OneNationUnderCopyright: The Golden Rule space station is run by the Golden Rule Corporation. The Manager is the one and only law, and if you don't pay your air tax, you get ThrownOutTheAirlock... [[SoylentGreen or worse]].
* PerspectiveFlip: In one alternate universe, Albert Einstein is seen as a villain worse than even Adolf Hitler, because he is blamed for the invention of nuclear weapons.
* PrecociousCrush: Gretchen on Luna develops a crush on Richard. She enlists in the Time Corps and ages up in a different timeline, just so she can bundle with Richard when she gets back -- a few months later from his perspective.
* PrivatelyOwnedSociety: The Golden Rule space station, and on Earth, some corporations have gained voting rights.
* RageAgainstTheAuthor: At the end, Richard rails against the kind of Author who would violate InfantImmortality by [[spoiler:killing a kitten]].
* RealityIsUnrealistic: DiscussedTrope. Richard is a retired colonel and tried writing war novels, but couldn't sell them because he wrote too accurately.
* RetGone: One of the members of Lazarus' TimePolice force is a Lensman. After he [[spoiler:shoots Richard]] in a fit of anger, they arrange to have him removed from existence. The effect is described as like seeing him rubbed out by an invisible eraser, followed immediately by the mortal wound that he inflicted vanishing.
* RippleEffectProofMemory: {{Discussed| Trope}} -- it fades after a while.
* SecondhandStorytelling: The FinalBattle against the rival time force is not narrated at all, but recounted via Richard's dictated journal recording, [[spoiler:which we are supposed to think is posthumous]].
* ShootTheShaggyDog: At the end, [[spoiler:Gwen and Richard are both wounded (Gwen severely), and have been left behind in the retreat from Mike's mainframe. They have no way of knowing if the mission was successful, and are certain to die if their enemies return to finish them off]]. Part of Richard's RageAgainstTheAuthor has to do with this.
* StagedShooting: Richard thinks that this has happened and that he's being framed for a fake murder. It turns out later to have been real.
* TimePolice: Lazarus has founded an organization of Multiversal sentinels whose mandate is to protect the integrity of history across multiple universes.
* TimeTravel: The massive overlapping use of this throughout the novel leaves the protagonist hopelessly confused at times, and by proxy, the readers.
* TimeTravelRomance: Played so casually as to be almost flippant, given the Burroughs device's capability to render time no more of a barrier to a relationship than walking a few yards. The most obvious examples include Gwen with Richard, Gretchen with Richard, and Lazarus with [[spoiler:Richard's mother]].
* TrivialTitle: The eponymous cat is a very minor character which shows up near the end and doesn't do much, apart from walking through a wall or two... [[ChekhovsGunman and, in doing so the last time, saves the mission from failure]].
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