[[caption-width-right:350:All right, who broke the camera?!?]]

->''"If we had an index file, we could look it up in the index file... under 'index file'."''
-->--'''Tegan''' discovers recursion

The one where Creator/MatthewWaterhouse throws up and the crickety-cricket celery wearer makes his debut.

Previously on the big Dee-Dub, the Doctor took a nasty spill from disconnecting the [[Recap/DoctorWhoS18E7Logopolis Pharos Project]]'s power cable, prompting a sudden regeneration. (It's a big one too -- [[SeriesContinuityError even his shoes regenerated!]]) Unfortunately, he doesn't take to it very well, and is in danger of turning senile; that is, unless he can get some rest and healing in the TARDIS' Zero Room, a sensory deprivation suite.

The freshly-regenerated Fifth Doctor wanders around his TARDIS with some regeneration amnesia, briefly and randomly adopting mannerisms from his past selves, constantly mistaking Adric for past companions, peeking into rooms and unraveling his scarf. The TARDIS is kind enough to hand her new Doctor a crickety outfit and a cricket room. Tegan just met the Doctor hours ago, and (though she took the whole new-body thing surprisingly calmly) even ''she'' realizes that he's gone batty. They get him into the Zero Room [[note]]which would be a great name for a nightclub[[/note]], but he's only just stretched out (three feet above the ground) and closed his weary eyes when the TARDIS' Cloister Bell alarm starts up. This is annoying enough for us humans when we're tired from a hard day slinging data and just need a good night's sleep before an important meeting in the morning; imagine how much it must suck if you're tired from saving the world and ''dying'' and being born again, plus the alarm isn't for an 8 AM meeting but an urgent warning that your spacetimeship is headed into the Big Bang.

Tegan and Nyssa put their heads together (as usual, Adric is being difficult ''and'' unwillingly in league with the villain), consult the TARDIS manual and inexpertly steer it to "Castrovalva: the Dwellings of Simplicity". Its brochure makes it sound like an alien day spa: the perfect place for a bit of R&R. The Doctor wakes up for a bit, and the TARDIS tries to help out by dumping a lot of random medicine on his head and providing him with a wheelchair. While spinning in circles in said chair and being extremely amnesiac, he instructs his companions on how to propel the TARDIS away from disaster by deleting rooms. Luckily, the control room doesn't accidentally get deleted. Sadly, the Zero Room does, so they have to improvise a new portable one out of some TARDIS doors [[note]](by using the Sonic Screwdriver as *gasp* a screwdriver; the amazing moment is available to buy at the BBC Store!)[[/note]].

Once they've landed and spent most of an ''entire episode'' carrying the Doctor through the woods, they discover that Castrovalva is... weird. It's built funny. All the books in the library are written in the same handwriting, even the very old ones. The quaint passageways always seem to lead to the same town square. Even more ominously, the kindly and wise elder statesman of the city is played by someone named "Neil Toynay", which of course is an anagram for "Tony Ainley", which means that the whole thing was an elaborate trap set by the Master! And they must escape Castrovalva as it dissolves into a puddle of Creator/MCEscher illogic around them.

Now ''that'' spells "regeneration trauma". No wonder the Tenth Doctor [[Recap/DoctorWho2005CSTheChristmasInvasion was bedridden and in need of a cup of tea]] after his regeneration. (And little wonder [[Recap/DoctorWhoS21E7TheTwinDilemma the Sixth Doctor spent his regeneration recovery trying to kill anyone and everyone around him.]])

Eventually, the Doctor regains his memory, convinces the townsfolk to override their collective WeirdnessCensor and defeats the Master. Also, it turns out that Tegan didn't steer the TARDIS at all - that was all the Master's doing. The Doctor pins a vegetable to his coat and happily heads over to the next adventure.
* {{Bizarrchitecture}} / MobileMaze
* ChasedByAngryNatives: You don't built a fortress on a impenetrable bluff if you welcome visitors. ZigZagged by the Castrovalvans themselves, who later reveal themselves to be a [[ProudScholarRaceGuy proud scholar race]] - underneath all the fur and feathers, of course.
-->'''Doctor:''' ..."Library"? ''Books'' and stuff?\\
'''Shardovan:''' (''dourly'') Books are [[CaptainObvious the principle business of a library]], sir.
* ChekhovsGun: Nyssa and Tegan pretend that the Doctor is still lying in the Zero Cabinet. They [[BondVillainStupidity know the Master well enough]] to predict he'll spend hours crow-barring the cabinet open rather then sticking to his plan. "One long last look before I destroy him utterly!"
** At first glance, the self-changing tapestry is mere artwork. The Master aims to turn it into the galaxy's biggest 3D printer.
* ChekhovsLecture: Tegan and Nyssa discuss recursion.
* ContinuityNod: The disoriented Doctor confuses his current companions for several previous ones, even going back to One's time when he calls Tegan "Vicki". He also takes on the mannerisms of the First ("I wonder, my boy, what you would do if you were me, hmm?"), Second ("Oh no! We've gone into the wrong part of the TARDIS! Jamie, you go back! When I say run, run!") and Third ("Won't be long now, Brigadier - if the Ice Warriors don't get there first!"), suggesting a sort of dementia.
** The Doctor's conversation with Adric (shaking his hand as if they'd just met, much to Adric's confusion) also counts as this. Adric is holding part of the Fourth Doctor's costume, which the Fifth Doctor has been discarding in pieces [[TrailOfBreadCrumbs to mark his path]].
---> '''Doctor:''' I left a waistcoat like that on... Ever been to Alzarius?
---> '''Adric:''' I was ''born'' there, Doctor.
---> '''Doctor:''' Really? It's a small universe, isn't it.
* ContinuityPorn: Some pinpoint the first major FanWank moment in the Classic series as being the Fifth Doctor's post-regeneration trauma causing him to go through impressions of all four previous Doctors.
* DemocracyIsBad: Used for the purposes of a gag.
* DistractedByMyOwnSexy: Averted this time around. The Fifth Doctor looks in the mirror, but his chief reaction is disappointment/alarm that the curls are gone.
--> '''Doctor:''' That's the trouble with regeneration... you never know what you're going to get.
* DistressedDude: Adric spends most of the story strung up in a web inside the Master's TARDIS.
* EasyAmnesia
* EstablishingCharacterMoment: The Fifth Doctor comes across as very gentle, very naive, and very ''normal'' for the majority of the episode, but after about three-quarters of the story, the "that's democracy for you" line firmly establishes him as a DeadpanSnarker as well.
* EverybodyLives: Well, nobody real dies.
* EvilWearsBlack: Subverted. Shardovan's the only Castrovalvan that wears black, which makes the rest of the characters suspicious...but he turns out to be a RedHerring.
* FakeMemories: Heck, the Castrovalvans have Fake ''History''.
* FallingChandelierOfDoom: Shardovan swings from a chandelier and crashes into the web, freeing Adric and breaking the Master's illusion.
* GettingCrapPastTheRadar: During the filming, Creator/MatthewWaterhouse had a ferocious hangover. Eventually, he ended up running over to a tree and vomiting during the scene where Tegan and the Doctor argue about who landed the TARDIS. The actors kept going so they could use the take. In the serial, if one listens carefully, Waterhouse can just barely be heard tossing his cookies off-screen.
* GigglingVillain: Anthony Ainley is quietly chuckling to himself all through this episode and [[Recap/DoctorWhoS18E7Logopolis the last one]].
* GilliganCut: The Doctor mentions how flying the TARDIS is difficult and you need to do more than flip a switch. Cut to Tegan, praying and flipping a switch.
* GlamourFailure: In truth, this was a barren jungle before the Master conjured up the city and its inhabitants.
* HeroicSacrifice: Shardovan.
* HiddenInPlainSight: The Master appear to be holding Adric captive in an undisclosed location elsewhere. The net is actually located right behind the tapestry, which explains how the Master could be in two places at once. The Master pulls this off twice: his TARDIS is camouflaged as the fireplace.
* IDieFree: Shardovan's FamousLastWords.
-->'''Shardovan:''' You made us, Man of Evil - but we are free!
* LeaningOnTheFourthWall: When the Doctor first sees himself in a mirror and talks to himself, it looks like he's addressing the audience.
* LivingBattery: Adric's block transfer computations are powering Castrovalva.
* TheLoad: Literally, in the Doctor's case. With the Zero Room lying in shambles, the Doctor and Nyssa contract a miniature version using a few leftover TARDIS panels. This makeshift Zero Room must then be wheeled all the way to Castrovalva. The Doctor promises that he will levitate within the box, thereby lessening the weight of it, but this (naturally) proves to be false as poor Tegan and Nyssa stumble around the jungle.
* Creator/MCEscher: The episode is named after an Escher landscape lithograph (not one of his eyeball-benders).
* MindProbe: The Master keeps Adric trapped in a hadron web that forcibly extracts Block Transfer Computations from his mind, and trying to force the Master out of his head seems to be [[TheWoobie pretty painful for the poor kid]].
* MindScrew
* TheNthDoctor: Creator/PeterDavison makes his debut as the Doctor.
* NiceHat: All of the Castrovalvans, but especially the Portreeve, who appears to be wearing a hat made of two Perspex boaters.
* NoOneCouldHaveSurvivedThat: The Master ducks into his TARDIS once his creations turn on him - but he's too monomaniacal to leave the web behind, so he gets tackled by the Castrovalvans as the city vanishes and buried them all (and his TARDIS) under solid rock. The Fifth Doctor doesn't address this, however, and even speaks of the Master in the present tense. He knows better.
* NotNamedInOpeningCredits: Creator/TomBaker doesn't get credited for his (archived) pre-regeneration appearance.
* TheNthDoctor: Creator/PeterDavison makes his debut as the Doctor.
* OurGraphicsWillSuckInTheFuture: It turns out that the fantastically advanced TARDIS computer has a display that is outperformed by a UsefulNotes/ZXSpectrum. Justified in that later it turns out that the whole interface was a phony produced by the Master so that Tegan and Nyssa would think they were piloting the TARDIS.
* PerfectPacifistPeople: The Castrovalvans who have evolved from a hunting society into a scholarly race. Justified in that it was all a trap by the Master, who knew that the Doctor would prefer to recover in a peaceful planet.
* PinchMe
* PlatonicCave: The eponymous Creator/MCEscher-esque setting, custom-made by the Master and PoweredByAForsakenChild, or Adric.
* ThePratfall: When the wheelchair supporting the Doctor's sarcophagus tumbles into a creek, Nyssa is sent to fetch it and winds up somersaulting into the drink, losing her mantilla in the process.
* RealityIsUnrealistic: People have often joked about the Doctor's regeneration almost failing, when all that happened to him is falling off a satellite dish, compared with some of his other regenerations. [[http://www.spike.com/video-clips/owmwa1/1000-ways-to-die-habeas-corpse Realistically, though]], it's a surprise he could ''talk'' after that...
* RedHerring: The audience is clearly intended to believe that Shardovan (who is shifty and sinister and dresses all in black) is the Master. Probably intentional in-story as well. Also, the Doctor encounters yet another primitive tribe, only to discover that they're friendly intellectuals who were honoring a supposedly ancient tradition.
* ResurrectionSickness: The Fifth Doctor had it bad. Probably the worst of any, barring perhaps the Eighth Doctor's. Made worse considering that his ship was headed into the Big Bang while he tried to recover.
* SceneryPorn: The picturesque Castrovalvan [[GhibliHills countryside]], which comprises a good deal of Part 2.
* ShaggySearchTechnique: The Doctor, still dizzy from his regeneration, bungles his first trip into the TARDIS and ends up the cricket room. Having shed most of his old clothes (and shoes) in the halls to avoid getting lost, he makes a jump for the cricket whites and gear on display. He's so taken with the result that it becomes permanent.
* ShoutOutToShakespeare: In his hazy state, the Doctor quotes ''Theatre/{{Hamlet}}'':
-->Go softly on!
* SignificantAnagram: The above-mentioned anagram for Anthony Ainley.
* TemptingFate: It's hard not to cringe at Five destroying his predecessor's scarf, as if Creator/PeterDavison didn't have enough of an uphill battle to get the fans to accept him in the role.
* TimTaylorTechnology: The TARDIS manages to survive the Big Bang. After jettisoning some rooms first.
* TomatoInTheMirror: For the Castrovalvans, especially Shardovan.
* TrailOfBreadCrumbs: The Doctor's companions aren't much use when it comes to navigating the TARDIS--though Five is, admittedly, foggy on the subject - requiring him to leave bits and bobs of the Fourth Doctor's clothing lying at intersections, so he can be found. Good thing that scarf was so huge. (Tegan uses her lipstick.)
-->'''Tegan:''' (''following string'') Looks like the Doctor's [[{{Pun}} coming unraveled]] in more ways than one.
* VillainousBreakdown: The Master has a meltdown after his precious web is destroyed. "My WEB! '''[[SkywardScream MYYYY WEEEEEEEEB!!]]"
* WeCanRuleTogether: The Master to Adric.
* WeirdnessCensor