Although the adversaries referred to in the story's title, the Chameleons, keep up a commendably icy and ruthless nature throughout most of the story, this turns out to create something of a false impression ultimately. They may talk a good fight ("I want him dead before Captain Blade returns"), and carry out some devious strategies (for example, replacing Polly with a double who claims not to know the Doctor and Jamie, thus helping to discredit their story) but they seem to become singularly compliant as soon as a definite advantage is established over them. The Chameleon duplicate of Meadows seems to virtually give up entirely once overpowered by the Doctor and company, and apart from one attempt to break free near the end of the story, co-operates fully and without protest. The Chameleon Blade also seems to accept the Doctor's judgement very meekly and resigns himself to the prospect of returning to his original blank form.

The Doctor's own lack of vindictiveness is also noteworthy. Once the struggle is over, and the advantage with him, he says nothing about punishing the Chameleons further, and even offers to help come up with an alternative solution to their problem. This although they have still caused a small number of deaths (what exactly did Crossland report after finishing his investigation into Gascoigne's disappearance?), and kidnapped thousands in their cause.

Indeed, the mass kidnappings pose a bit of a question which is never quite satisfactorily answered, that being, why did no-one else apparently notice that their loved ones were missing? Samantha turns up to enquire into her brother's disappearance, but we never hear anything to suggest that any of the others have been missed. Are they all supposed to be still on holiday? Of course, that raises the issue of how long the Chameleons have been carrying out their operations in the first place (not all that long, presumably).

Apart from the supercilious coolness Donald Pickering brings to his Captain Blade, the actors who make the most impression here are Pauline Collins as Samantha (Sam), Colin Gordon as the Commandant, and Bernard Kay as Crossland. Sam has an engagingly chipper quality, and is very brash and self-confident for this part of the series' history. Like Dodo, although more successfully, her "working class authenticity" is denoted by a strong regional accent (Liverpudlian, which the various Merseybeat groups of the time had helped make fashionable), and she throws herself into the story with unabashed enthusiasm. Jamie seems rather taken with her as well, and she isn't shy of taking the lead in sharing a kiss or two with him. Whether this more upfront side of character would have lasted had she become the full-time companion that was originally intended is difficult to say, so while she might have been a missed opportunity in one sense, it may also be as well that the character was never in a position to be diluted.

Colin Gordon gives a particularly well-judged performance in his role, managing just the right sort of fussy pompous charm. As the story's main sceptic (fulfilling a similar function to the authority figures who turn up in the various base-under-siege stories of the era), he is deliciously sarcastic towards the Troughton Doctor's wildly improbable and unconvincing claims, and it's easy enough to understand his evident exasperation with the latter. Although it's also quite charming that once the whole story is out in open, he becomes as loyal and steadfast in his support as anyone could wish for, even managing to take the initiative and both buy the Doctor time and help save the day. Bernard Kay is also quietly impressive as the stolid and well-intentioned policeman, even if he seems remarkably ready to accept the Doctor's outlandish claims.

The Doctor's own status as an outsider and non-conformist are brought to the fore here in various ways, most notably his dismissal of passports as "some sort of official mumbo-jumbo" and his unwillingness to tolerate having to meet the various bureaucratic requirements of the airport when trying to report Gascoigne's murder through legal channels. Very much the free spirit who is used to travelling when and where he likes, he is often in need of an official representative of the authorities to intercede for him (Crossland fulfils that function in this story's case), but on the other hand it does hive him the advantage of having a much wider frame of reference than the others and make deductions they would never think to (such as when working out what the aircraft's stationary status on the radar signifies). Although even then this can cause problems as to how likely anyone is to believe him.

The story tends to ramble a little and is possibly overlong (there are a lot of escapes, captures, near captures, traps sprung and evaded), as well as being slightly spoiled by the regular use of naive-sounding terms like "ray gun". As a variation on the concept of aliens stealing bodies or identities, it's one of the more interesting in the series, and benefits from some assured acting, and appropriately sinister music and sound effects. In some ways the (for its time, unusual) contemporary setting makes it seem more, rather than less, fantasy-based than its immediate neighbours.