But the introduction of Janet - Number 6's fiancée - to the series goes so contrary to everything established previously about Number 6's character that this, combined with the absence of McGoohan, does not feel like The Prisoner we know.
Nigel Stock does an admirable job in Number 6's place but he is working against the material and he is constantly in the shadow of McGoohan's portrayal. He gets a couple of strong scenes, first of which is the scene where he confronts Sir Charles Portland, who seems to be Number 6's former boss and father of his fiancée (never mind that he, like Janet, has never been referred to before in the series).
Sir Charles counters every attempt by Number-6-in-the-Colonel's-body to convince that he really is Number 6 with the argument that any information he provides to establish his identity could have been extracted from the 'real' Number 6 and learned by him.
Sir Charles's skepticism is contrasted with Janet's faith in Number-6-in-the-Colonel's-body, in a moving scene where he is forced to rely on her trust in him even though he looks different. This pays off for him.
As a one-off spy/sci-fi drama this could have been decent, looking at the question of identity and how something like Seltzman's machine would affect it, and the role of trust in such a scenario, but to me it doesn't fit The Prisoner.
The nadir of the episode, production-wise, must be the ridiculously bad wig on Nigel Stock's stunt-double during the fight scene before he and Seltzman get taken to the Village. I don't normally notice things like this but this was a particularly obvious example.
On the positive side there are a couple of amusing in-jokes, such as Sir Charles asking to see slide "number 6" during the pre-titles sequence, or the man in Austria greeting Number-6-in-the-Colonel's-body with "Oh, welcome to the village sir."
The twist at the end - the three-card-trick performed by Seltzman with three minds - is clever, but again I have to come back to the fact that in the context of The Prisoner, as established by previous episodes (as far back as Arrival), Seltzman-in-the-Colonel's-body is hardly going to remain free for long.
This brings to an end a run of weaker episodes. I think The Prisoner was perhaps losing its way somewhat by this point, even if a lot of the flaws with Do Not Forsake Me Oh My Darling can be put down to the lack of McGoohan both in front of and behind the camera - I can't imagine him approving of the inclusion of a fiancée for Number 6, even if the only time they kiss it's another man doing the kissing.
Next: Living in Harmony