So we're back--for this story--to BritBox, with its nice, crisp copies of the episodes in question, and, yes, it's a relief to be granted a reprieve from recons, helpful though they are.
Aired in March, 1966, The Ark has two great ideas at its core, but only one gets any traction. The first idea, that of the "sleeper ship" voyage gone awry, dates at least back to A.E. Van Voght's Far Centaurus (1944), and this story arc bears some generic resemblance, but actually is more reminiscent of "Think Blue, Count Two" by Cordwainer Smith, published in 1963. (In point of fact, Robert Godard postulated just such a "colony ship in 1918, but as that manuscript wasn't published until 1972, it's de trop for our purposes.) There, as here, the millennia that have passed (though not, in The Ark, due to the voyage (not too long under way, expected to take 700 years), but rather to the TARDIS's usually long time jump from the end of The Massacre) have created problems of comprehension and of lost knowledge posing a risk to the voyage's safety. And of course the notion that the common cold could be deadly to the higher evolved beings dates back to Wells's War of the Worlds (1897), though, of course, in that novel it defeats the otherwise unstoppable Martians. (The Martian's last signal, "uless") has stayed in my mind since I first read Wells as a boy.)
But what this story really reminds me of, as if the clip up top didn't give it away, is Pierre Boulle's Planet of the Apes, not filmed until 1968 (also de trop, accordingly), but published in English under the title Monkey Planet in 1963, so it could have influenced the script. Possibly. The Ark is a bit of a mashup--the colony ship carrying micro-reduced humans and their servants, the Monoids, at first welcome the travelers, showing them a partially built (up to the knees) statue of a human being that they work on to keep the importance of their mission to preserve all life on Earth (about to be consumed as the Sun becomes a gas giant). The welcome turns sour though, when the mission is endangered by Dodo's cold, to which the Ark's pilots (Guardians) and Monoids alike have no immunity. The humans are divided in their response--some, like the Commander and his daughter, believe that the rapidly spreading plague was accidentally transmitted by Dodo, and that the Doctor, Steven and she are well-intentioned, as well as being the best hope for curing the plague, and the mob, goaded on by the second in command, Zentos:
Zentos: I invoke the special galactic law against them. Hold them, take them into custody and later they will be made to answer for the crimes that they have committed.. The silent Monoids merely seem grieved for those of their number who succumb. The Commander, aided by his daughter Mellium, countermands the credit and sentence of execution of the Doctor and his party. The Doctor experiments on Steven, finds a cure, and all is seemingly well. The travelers leave, and....
Steven: Oh, listen to us!
Zentos: Take them away!
Mellium: What about my father?
Zentos: He may well die. But then again, so might all of us. In which case it was pointless leaving.
Steven: That unfortunately tells me only one thing.
Zentos: What's that?
Steven: That the nature of Man, even in this day and age, hasn't altered at all.You still fear... the unknown like everyone else before you.
...the TARDIS reappears in the colony ship, 700 years later, shortly before the landing on the new planet. The bridge of the ship is largely abandoned, weeds and vines allowed to infiltrate, and the completed statute--
Has a Monoid's head.
Well, you can see the similarity--once the docile, silent animal-like servants, the Monoids are now the masters, keeping a few Guardians around simply to enjoy being served. Not entirely dissimilar to Boulle's novel, if rather different from the film. (Though one wonders if the use of the statute to indicate visually the radical shift that has taken place in The Ark had any influence on the similar use of the Statue of Liberty at the end of the 1968 film Planet of the Apes. Probably not, but interestingly prophetic, no?)
The Doctor, Steve and Dodo (now wearing Ian's tabard from The Crusade, for no adequately explored reason, though it does suit her), try to inspire a revolt, but fail:
The Monoids intend to bring their own kind only down to the planet, and leave the humans, both awake and preserved, onboard the Ark, which is set to explode 12 hours after the Monoids leave.
It is only with the help of the natives of the planet, invisible, incorporeal beings with extremely strong telekinetic powers, and the fact that the Monoids begin falling out among themselves, that peace is, uneasily restored. The Refusians, or perhaps we should call them the Deus Ex Machina, or even Trelane's parents (no, they're still a year off), have readied the planet for the colonists--it needs life, they think--but will only allow the humans and Monoids to stay if they make peace. With the humans in the ascendancy again, they agree to live as equals with the Monoids.
It's interesting that the Monoids come off rather well in the first half--they are dignified, and do not join in the mob against the Doctor and his companions, but are genocidal in the later half. Of course, their more cruel leaders are all dead by the end, and the Monoids remaining to be revived are from the era of the first half, so there is hope for peace. Maybe.
Not for the Doctor, though. As the TARDIS lands, with both Steven and Dodo modeling new, psychedelic clothes (Jackie Lane as Dodo pulls her off; Peter Purves somewhat less so), the Doctor disappears, his disembodied voice warning them that they are under attack....