Whilst the ratings for The Web Planet were high, the Reaction Index went on a decreasing slide week after week.  Things started brightly enough, with a rating of 56% for episode one (an improvement over The Romans, although a few points lower than most of the Doctor’s space adventures to date) but by episode six the figure had tumbled to 42% (the lowest RI rating the series had received so far).

It’s not hard to understand why the general reaction was so unfavourable.  As I said earlier, had it been a four-parter they might have just got away with it, but by Invasion there’s a real sense of treading water.  Watching Hartnell turn a Zarbi into his compliant pet does have a certain comedy value, but these moments only stretch so far.  Vicki’s quite taken with the friendly Zarbi though, nicknaming him Zombo.

But although parts of the story are painful and/or dull, there are still some occasional lyrical moments of scripting which almost makes it all worthwhile. In this scene, Prapillus (Jolyon Booth) and Barbara enter the temple of light.

BARBARA: It’s beautiful, Prapillus. Oh, it’s absolutely beautiful!
PRAPILLUS: It must be a Temple of Light. The ancient song-spinners of our race sang of their beauty, but I thought they could never be found again.
BARBARA: There are others?
PRAPILLUS: So the legends say. Sewn into the craters and plateaus of Vortis, been slowly un-woven by the silence of time and their entrances long forgotten by our species. But our Gods have not forgotten us, Barbara. This was indeed deliverance.

Another positive part of the serial is that Barbara, thanks to her association with the Menoptera, is probably the most proactive of all the TARDIS crew.  Although visibly frightened by the events of episode one, she quickly recovers and teams up with her new friends in order to find a solution to beat the Zarbi and the Animus.  The downside is, of course, that she spends most of her time surrounded by the ridiculously overacting Menoptera, but then you can’t have everything.

Something that’s noticeable about Invasion is how little ambient noise there is.  A slight echo effect is given to the cave and tunnel sets, but that’s about all.  Combined with very minimal incidental music it does create a rather “dead” atmosphere.  One plus point is that there’s very little Zarbi chirping in this one – although when that’s removed they do seem even less convincing than before.

The Optera make another appearance.  Pity anybody who happens to be watching these scenes when a non-fan enters the room.  How would you be able to explain them?  Not easily, that’s for sure.  But even though they still look very silly, as with Prapillus there’s the odd inspirational moment of dialogue.  “A silent wall. We must make mouths in it with our weapons. Then it speak more light.”

Whilst Barbara’s raised several possibilities about how the Menoptera could fight the power of the Carsinome, it’s only when she’s reunited with the Doctor and Vicki that the planning can begin in earnest.  The Doctor takes instant control in a very characteristic way.  He and Vicki then elect to return to the Animus, which provides us with a very unsettling cliffhanger – the pair of them are frozen into solidity, surrounded by gently bobbing Zarbi.