The one where the Doctor is a walrus. Koo-koo kachoo.
The TARDIS heads for the future again, and manages, because of a Timey-Wimey Ball, to arrive at a space museum. The museum displays the conquests of the great Morok empire, and the planet is Xeros, one of the many under the dominion of the Moroks.
Team TARDIS sneaks around the museum for a while, before realising that they're invisible, inaudible, and also that later versions of them are trapped in glass display cases as museum exhibits. Vicki, impressing the Doctor with her understanding of dimensional physics, realises that they've jumped a time track and they're all stuck in a reality that might or might not lead up to them becoming Human Popsicle displays. The group decides to mess with time and stop that possibility from becoming reality.
Time sorts itself out again, and then the TARDIS properly arrives on Xeros. The Doctor is soon captured, and entertains himself by effortlessly outwitting the Moroks' mind-reading machine. Ian and Barbara spend a lot of time walking through corridors and trying to find the exit. Vicki falls in with La Résistance, the native Xerons, who want to rise up and free themselves from the Moroks. She helps them by hacking into the security system and getting them some proper weapons.
In the end, the Xerons and their magnificent eyebrows win the day, the heroes don't end up in display cases, and Vicki has a bit of a Friendship Moment with their leader before departing again. As a souvenir, the Doctor is given a giant Time And Space Visualiser: a sort of omniscient TV set.
As the travellers depart, we cut to a deserted planet, where a Dalek reports that the TARDIS is underway, and is told that the Daleks' own time machine is in pursuit and the Doctor will soon be exterminated.
- Absentee Actor: William Hartnell was on holiday for Episode 3, so he only appears in the reprise of Episode 2.
- All Cloth Unravels: The museum is labyrinthine enough that Ian unwinds Barbara's cardigan in order to use the wool à la Theseus. To be fair, he is shown to have some trouble starting the sweater's disassembly, and Barbara has to take it from him and pick open a starting point; but after that it's just treated as a ball of yarn with a long single thread (which, as usual with string in a labyrinth, runs out too soon).
- Anti-Sneeze Finger: While the TARDIS crew are hiding from a guard patrol, Vicki feels a sneeze coming on, and Barbara holds a finger under her nose. A few seconds after Barbara removes her finger, Vicki sneezes loudly.
- As You Know: The second episode is notorious for this. After a really scary and surreal first episode in which the characters wonder around an invisible museum and witness their own corpses, the second episode kicks off with an overweight, middle-aged Rubber-Forehead Alien delivering a ton of Call a Rabbit a "Smeerp" Technobabble beginning with "As you know...". This is a rare example of the speech managing to be unnecessary to the other character and incomprehensible to the audience at the same time. Helpfully pointed out by Robert Shearman on a DVD special feature, in which he ponders whether the sequence is "badly written" or "amazingly badly written".
- Brief Accent Imitation: While hiding in a Dalek shell, the Doctor amuses himself by impersonating their voice.
- Dead Guy on Display / Discovering Your Own Dead Body: Which tells the party that they had best leave before they end up like this.
- Discovering Your Own Dead Body: The Doctor and his companions land on a planet but they're Just One Second Out of Sync. While they're out of sync they wander around the museum and find their own preserved bodies on display. When the timelines resync they go on the run from the authorities to make sure that they don't wind up dead.
- Distressed Dude: The Doctor has to be rescued by Ian after getting Strapped to an Operating Table to undergo a form of artificial death
- Electronic Telepathy: A machine the Doctor's interrogator uses is supposed to do this, but the Doctor is able to send false images.
- Invisible Main Character: The Doctor and companions throughout Episode 1.
- Just One Second Out of Sync: The TARDIS crew immediately after landing on Xeros.
- La Résistance
- Lie Detector: The door to the armory is linked to one. It only opens when someone can truthfully give the right answer to all of its questions. At least, until Vicki reprograms it.
- Long List: The list of questions the armory door asks.
- Living Museum Exhibit: The TARDIS 'jumps a time track' and the Doctor and his companions find themselves in the eponymous museum and at some point in the future where they have become exhibits.
- Meaningful Name: In the documentary "Defending the Museum" Rob Shearman says the Morok's name shows they are morons.
- Mind Probe: The Moroks subject the Doctor to one, but he cheerfully subverts it and causes it to display a succession of irrelevant images.
- Nothing Is Scarier: The crew get caught in a TARDIS technical fault in which they are unable to interact with or see anyone, can't leave footprints, and time occasionally flows backwards or skips ahead of events they have no recollection of doing. It is very spooky and atmospheric and especially stands out when the rest of the serial is a fairly light-hearted comedy story.
- The One Where Everyone Dies: Revolves around the crew attempting to prevent their forseen deaths.
- Ooh, Me Accent's Slipping: Richard Shaw, who spoke with a Cockney accent, was cast as Governor Lobos, but was asked to deliver his lines in BBC English. His accent slips only once, when he bellows at an underling to use "maximum securi'ee!"
- Psychic Static: When asked how he arrived in the museum, the Doctor thinks of... a high-wheel bicycle. And he imagines a group of walruses when he is asked where he is from.
- Psychotic Smirk: The Doctor gives one when he's teasing his torturer with a Psychic Block Defence.
- Reckless Gun Usage: Ian and Vicki with the rifle they find in the museum. Especially Vicki walking around holding it under her arm with the end of the barrel tucked into her armpit.
- Refuge in Audacity: how Vicki gets into the Morok armory.Armory Computer: Purpose for which the weapons are required?Vicki: Revolution!*door opens*
- Scare Chord: Three times. First when they notice that they don't leave footprints in the sand, again when they see the Dalek casing, and once more when they notice their bodies on display.
- Screw Destiny: From Episode 2 onward, the TARDIS crew's goal is to avoid being trapped in the museum cases.
- Self-Fulfilling Prophecy: The characters worry throughout the serial whether their actions to try to avoid their fates are in fact bringing that fate closer.
- Slave Race: The Xerons describe themselves as such.
- Sneeze of Doom: Vicki tries to hold in a sneeze while the gang are hiding from the Xerons. Barbara stops her the first time, but then she makes a loud one. However it ultimately doesn't matter, as nobody can see or hear them anyway.
- Stock Footage Failure: Happens in-universe when the Doctor is hooked up to a mind-reading machine so his captor can find out where his companions are using pictures extracted from his memory. The footage extracted this way is useless because it shows where the companions were when he left them a long while ago, not where they are now. By this time, he's figured out a Psychic Block Defence and so, when pressed harder, the screen starts producing deliberately ridiculous stock footage of sea lions, etcetera.
- Tempting Fate: Ian's comment about hoping to never see the Daleks any time soon.
- Timey-Wimey Ball: the theory of time travel used in this story is unclear. At some point, the Doctor and his companions landed on Xeros and through an unknown sequence of events were turned into exhibits for the Moroks' museum. They also arrive, walk around on Xeros while not really being there at all while an instrument in the TARDIS is stuck, and then when they finally "arrive", the display cases disappear. It almost appears to be a case of the TARDIS offering a glimpse into an alternate possible timeline rather than something that actually happened as a result of time travel.
- The Doctor specifically mentions that they (the them out of the casings) are in a different dimension of sorts, looking into this dimension where they are all on display. We know dimension travel was possible before the Last Great Time War, so this is the more likely explanation.
- Considering how much the TARDIS likes the Doctor it could have deliberately jammed itself so the Doctor could see this timeline and prevent it.
- Trail of Bread Crumbs: Ian gets the idea of unravelling Barbara's cardigan to mark the corridors when they get lost in the museum, like Theseus.
- Unusual Eyebrows: The Xerons have these
- Vestigial Empire: The Moroks used to have a great space empire but they have become decadent and bored. Lobos points this out and the Doctor compares it to the Rise and Fall of the Roman Empire.
- Wham Line: Ian states just a bit ago that everyone's walking on dust. Normally, this would be nothing more then a Captain Obvious moment, but he then he points out something not so obvious: "Then why aren't we leaving any footprints?"
- What Happened to the Mouse?: There's a scene where the Doctor obsesses about Ian losing a button from his cardigan, prompting Ian to ask the Doctor why he's always so interested in such trivial things. The Doctor tells him in a significant way that trivial things often lead to great discoveries. The button never comes up again. This was observed by Robert Shearman on a DVD special feature, who called it 'brilliant'.