Normally, in a Dr Who story involving monsters of some kind, the threat will be perceived as one from outside attacking an unsafe centre. The base under siege stories that comprise a fair fraction of the Troughton era are one example, as are the Earth invasions (or variants on the formula) used in the UNIT adventures. This story is of a less common variety, depicting a society that is already under the thumb of malevolent forces and has been for generations.

Moreover, it's a society which doesn't actually realise it has been taken over for someone else's ends. Most of the people seem to take it for granted that their society is genuinely being run for their own benefit, mistaking exploitation for privilege. In this respect, the story is similar to The Macra Terror and State Of Decay, and arguably it could even be said to foreshadow similar concepts in The Long Game and Bad Wolf.

Here, the psychology of it is thought through fairly cleverly, with the Gonds eagerly vying for the approval of their unseen masters, apparently seeing the reward granted to the best students (becoming "companions of the Krotons") as a great honour. Even by the terms of their limited understanding of the situation, the process can be seen to involve self-sacrifice, with the winners being permanently separated from their family and friends, indeed from anyone who ever knew them. It testifies to the quasi-religious terms the Gonds appear to view the Krotons in. Spending the rest of your lives in their company is seemingly the destiny that most transcends ordinary day-to-day living there, the best future anyone can hope for, and the highest service a Gond can perform for their society's good. It is compulsory to join them in the Dynatrope once summoned, but it hardly needs to be. The Gonds seem to regard it as unthinkable that anyone could not want to anyway.

For that matter, they seem to regard various subjects as unthinkable. If the Krotons have refused to teach them about a subject or forbidden any knowledge of it, the Gonds appear to take this judgement for granted and closed themselves off from pursuing or taking any interest in it. "Did it never occur to you to wonder why?", as the Doctor asks Selris at one stage. Again, it is a matter of the Krotons ensuring they can retain the upper hand by lessening the Gonds' chances of being able to develop any science with the potential to harm them, a tactic the Doctor deduces when musing on how significant the gaps in their education might be. Beta also later expresses his frustration at being fed information from above "like a dog, with scraps" rather than investigating and gaining knowledge for himself.

The turnaround in the Gonds' attitudes to the Krotons is effected by the arrival of the Doctor, Jamie and Zoe, and what they witness. As random elements introduced to the setting, they are able to disrupt a routine that has been going on for generations by providing proof of what becoming a "companion" to the Krotons really involves. This turns out to be a catalyst that splits the Gond society into competing militant factions, whether students trying to smash the machines in the Hall of Learning, or Eelek abandoning his previous loyalty to the regime and plotting a rebellion, pitting himself directly against Selris, or indeed anyone who doesn't seem to feel sufficient enthusiasm for his cause. This can be seen in his confrontation with Beta, whose scepticism and appeal for more time to develop a possible weapon are angrily shouted down. Having been disabused of the Krotons' true nature, Eelek no longer sees them as a means to power and influence for himself but an obstacle, so they have to be fought and destroyed as soon as possible. And anyone who disagrees with the strategy, even if they agree as to the ends, is also an obstacle to his ambitions, hence also an enemy.

Thara, the other main element in the power struggle between Selris and Eelek, is unfortunately a rather cliched "hotheaded rebellious young man" stereotype (and overacted, too), and once his girlfriend Vana's main plot function (as a narrowly surviving victim of the Krotons) is over, the two of them become little more than a standard pair of "heroic allies" for the Doctor's party. However, his apparent determination to replace Selris as leader after the latter's death, and insistence on the hereditary principle, in defiance of Eelek's attempt to seize power for himself, suggest that the story is taking an anti-revolutionary line, despite the "consciousness-raising" implications of a society freeing itself from an entrenched and institutionalised source of repression. While Eelek is painted as power-hungry, unscrupulous and callous, and does not give the impression of being morally fit to lead them, it feels slightly odd and somewhat fairytale in nature to imply that re-asserting the old system of hereditary leadership (which on the strength of Selris's largely ineffectual example, is not necessarily guaranteed to produce the best leaders) is going to solve the problem in itself.

Visually, the story tends to lack interest at times, with some rather dull sets and costume designs for the support cast (Selris excepted: his clothes appear to be intended to mimic a Kroton's appearance), although the darkly lit Learning Hall has a certain atmosphere and texture. The other main exceptions are the sets for the Dynatrope, which do have a highly stylised State-of-the-art feel, and the bizarrely designed title monsters, with both being themed around pentagonal or hexagonal shapes. There are some bracingly psychedelic-feeling effects and sequences, most obviously the sensory ordeal which the Doctor and Zoe undergo on first entering the Dynatrope, with distorted camera angles and abstract images. The Krotons themselves are a memorable creation, being lumbering crystalline creatures speaking with strangulated accents that seem to sound slightly like Birmingham or Afrikaans ones at different times. They only appear from towards the end of the second episode, and so are only really seen for the space of about two episodes, and when active they tend to function as fairly generic monsters. The nature of their existence, where they can be constituted and dissolved in crystal slurry, is more interesting than anything they actually do.

Among the regulars, it's not an especially strong story for Jamie. He gets to have a fight in the first episode, but is thereafter often given the role of running about after the others, having to do what he's told, getting into trouble and so on. The Doctor and Zoe's competitive relationship is brought to the fore very well though, especially in the scenes where the former bumbles through tests that Zoe has already passed easily enough. His pointed comment about Zoe being a genius ("It can be very annoying at times!") also points towards it. He seems to take a mild glee with being able to outfox her or leave her guessing about matters she knows less of than him, whether it be the presence of the HADS control to rescue the TARDIS from dangerous situations, or his (intentionally?) misleading comment to her about Jamie which could be mistakenly read as an implication that the two of them are about to leave the planet and strand him there. There's little real antagonism there, the two of them are clearly fond of and close to each other, but within those bonds, there is some scope for occasional edginess. Patrick Troughton and Philip Madoc give probably the best acting performances, the former managing a dry charm, with a gentle quality that comes to the fore in the scenes where he is tending Vana. The latter attacks his role with a truculent gusto.

The realisation of the story is creaky at times, but it remains a reasonably interesting science fiction story within the series' format, at least beneath some of the genre clichés and unenthusiastic acting.