There are stories where the elements are melded together in a way which prevents the plot seeming contrived and artificial.  Or there are stories like this one, where too much of what happens just seems to do so because the writer wants it to, rather than because it flows naturally from the action.

For example, the Cybermen have a base under the sewers in London.  Why?  There's no apparent reason for them to be there within the terms of the story itself, other than to kidnap and convert anyone who happens to wander nearby. Even the later revelation that they have found a time machine (origin unknown) and are planning to divert the course of Halley's Comet doesn't really justify going to all the trouble of setting up a secret base on Earth, unless perhaps they're intending to use a tractor beam of some sort (and even then they could do so from a ship flying close by the planet).

It's been stated, apparently, that part of the authorial intent concerning them was that they were survivors from the Troughton story, the Invasion, which is even less convincing, for several reasons (it makes nonsense of the intent of the earlier story for one thing, and it's barely credible that they would sit it out there for years without making any serious attempt at building new forces and attacking the centres of power, especially if they've still got a ship hidden behind the moon, as Lytton claims, plus it's an explanation which relies on being aware of the other story in the first place).  Nor is it entirely clear whether any are still there by the end of the story.  Presumably they do all return to Telos in the TARDIS in the second episode, as that otherwise be a rather messy loose end.

The idea of Lytton being stranded on 1980s Earth and  using ruthless means to achieve his aims is an interesting one, but his methods as shown still raise questions.  He has apparently established contact with the Cryons and finalised their mutual plans, but as they are far in the future, how can the simple distress call he's set up achieve that?  Presumably the signal is being beamed through time as well as space (especially as the TARDIS also picks it up) and, while that might be possible given that Lytton himself is a product of a more technologically advanced future society (and on those grounds he's got a better excuse than Whitaker in Invasion of the Dinosaurs, who seemingly managed to construct similar technology on the same resources).  But a distress signal is not normally a means of having a two-way conversation (would the Cryons have any means of transmitting back into the past in reply?  they don't appear to have any time travel-related technology themselves).  Pe rhaps the Doctor simply misunderstands the nature of Lyttons' device and mistakes it for a distress call?

It's also not clear why, if he is intending to meet the Cybermen and get taken to Telos, Lytton doesn't simply turn off the signal, as it's obviously fulfilled his purpose.  He doesn't need to use it to communicate with the Cryons again, and would be aware that voluntarily going into the Cybermen's custody means he almost certainly will never get the chance to use it again anyway, so what reason has he got to keep it transmitting?  If he's cautious enough to set up relays concealing the signal's origin, he may as well switch it off and save himself the trouble.  The only reason I can think of for keeping it on in the circumstances is the possibility that it might attract the Doctor, and Lytton's statement to the Cyberleader that he's "been expecting him" could maybe be a hint that he was always planning for the Doctor to get involved, perhaps in the hope that the TARDIS would be an extra bit of insurance, and that the Doctor might either provide some help, or failing that, function as a diversion to occupy the Cybermen's attention while he, Lytton, gets on with the plan.  However, that really would be trusting to luck in the extreme, especially if he's hoping he picks up the signal on exactly the right day.

Once Lytton's plan does get going properly, it does bring out some of the more interesting elements of the story though. The Cryons are a slightly underrated alien race, I feel, whose overly twee an soft-spoken voices go some way towards hiding what seems to be a rather hard-nosed and unsentimental streak. Happy to do business with ruthless mercenaries (and make use of their skills) to get what they want, and in a way that involves little or no risk for themselves, they also have a nice line in pointed laconic remarks (effectively telling the Doctor to push off before he's the occasion of any more deaths, right at the end of the story). There's an interesting possibility that the Cryons may have undeclared ambitions of their own for the Cybermen's time machine (perhaps as a means of trying to prevent the Cybermen's original colonisation of their planet) despite their claims to be concerned only with avoiding the disruption to the time line the Halley's Comet plan would cause. On the other hand, their apparent lack of interest in using the TARDIS for anything like this after their plan with Lytton fails suggests not (unless they simply decide the Doctor would never agree, and that they wouldn't be able to operate it without his approval).

The characters' various priorities do seem a little obscure at times. Lytton presumably just wants to escape from Earth and sees the time machine as being as good a ship as any, especially if it can return him to his own era. His protestations to the Doctor are probably a little insincere then, as he's really just doing a job for payment. In any case, if he comes from a future Earth colony (which is suggested by the way he talks to Griffiths of their mutual ancestors crawling out of the primeval swamp) then he has as much of a personal stake in Earth surviving past 1985 as Peri does, more even, as it prevent his from having even been born. Still, it's rather neat that it should be Lytton who picks up on Peri's instinctive selfishness when, just after worrying about the Earth's fate she dismisses some other (genuine rather than putative) victims of the Cybermen (Peri: "I'm not interested in the Cryons"/Lytton: "There's compassion for you.").

That said, the Doctor's attitude to Lytton is rather vindictive, as the latter points out, and indeed somewhat inexplicable, considering that the two of them barely met in their previous adventure, with the Doctor never even learning his name. Plus, of course, the Doctor would have known that as a Dalek-controlled duplicate, he could have had no way of telling whether or not Lytton's apparent personality was his genuine one, bearing in mind how different a person Stein was when his conditioning lapsed. Only an untelevised encounter between these two stories would really be able to explain how the Doctor is able to react so forcefully and immediately to the mere mention of Lytton's name.  The fact that Lytton doesn't try to take the Doctor into his confidence while they're prisoners in the TARDIS isn't really a mark against him, as he can't be certain the Cybermen won't have had the room bugged, and he has little chance to do any explaining again before the chance to escape arises.  So the Doctor is right to a degree about having misjudged Lytton although it would be a mistake to get too sentimental about him.  He's not as lacking in integrity as the Doctor initially believes, but is still clearly a ruthless self-interested man who thinks nothing of sacrificing others for his plans.

So although Lytton's final capture and attempted Cyber conversion can evoke some pity for him, it's still also a fate he's deliberately engineered for others beforehand (the men he takes on his faked bank raid), even if his giving the Doctor the sonic lance ultimately helps save the day (the hand crushing sequence, incidentally, looks suspiciously like an attempt at repeating the impact of the scene in Androzani where Jek has two androids try to tear off the Doctor's arms).  It's a little odd that the Cybermen never do attempt to convert Griffiths, incidentally, unless they're simply planning it later (as he's no use to them otherwise), although Brian Glover's likeable portrayal of the latter does help to add a more grounded and humorous perspective to all the exposition (which, in the second episode in particular, seems interminable) and running around.

The Cybermen don't don't come across as particularly intelligent here.  Their Halley's Comet plan (apart from feeling like a tacky way of cashing in what was then an approaching phenomenon) seems a bit of a silly way of preventing Mondas's destruction (especially as that took place in the Tenth Planet because of an energy drain.  Taking Earth out of the equation in 1985 would only buy Mondas a little more time at best).  It would make more sense to intervene directly with Mondas's own past in some way if that's what they're most interested in. 

Also, locking the Doctor in a cell full of explosive (which only needs heating to work) and a fellow prisoner to fill him in on the rest of the plot, seems inept in the extreme.  There again, this could be an example of how beings guided by logic aren't fully able to counter or anticipate the strategies and tactics of less rational than themselves, although it's still something of a convenience.  It's also unclear how they got Flast into the cell (presumably she was transported within a container of some sort, as she dies on exposure to the air and temperature immediately outside it) and why they're bothering to keep her alive (for future interrogation?  Or do they also convert Cryons into Cybermen?)

There is a neat touch at one stage though, where the Cyberleader practically taunts the Doctor that he understands integrity and compassion more than the latter, in that the Cyberleader has been thoughtful enough to provide Peri with warm clothes to help cope with the cold on Telos, whereas the Doctor has been plotting against him (although presumably the clothing is just a means of ensuring she doesn't die of hypothermia before she can be of use to them).

The production values are mostly very good, lending the grey Telos exteriors, gloomy sewers, 1980s London scenes, and cold underground base a distinctive flavour of their own, although Cyber control itself has a tendency to look rather tacky and plasticky.  The music veers from moody and sinister (the sewer scenes) to jarringly intrusive and overdone (some of the London locations).  Maurice Colbourne gives the only acting performance of any real note, lending his character a deadpan charisma and commanding screen presence that helps to keep up some interest in the proceedings.

On the whole, the story is rather superficial and not very well thought out, although effective at times, and is of most interest both for its attempt at depicting the Cyber conversion process to a greater degree than had been seen before, and for its development of the antihero character created for Saward's previous story.