Uh oh, it’s the Optera. Underground cousins of the Menoptera, they look and sound ridiculous. During this story they’re hardly alone in that, but it was their hopping movements which proved to be the final straw for me. This is a pity, as their dialogue has promise. Here, Hetra (Ian Thompson) outlines the Optera’s philosophy. “We know that from the roof comes hate! The liquid death! Creeping destroyer of we Optera. Yet you stand upright. We will consult the chasm of lights and if you come from above, you will die!”

Last episode was quite Menoptera light, but they’re back in force in this one. That means plenty of dialogue delivered in a sing-song manner and excessive hand movements. And as the majority of the episode is set on the planet’s surface, it’s back to the vaseline-smeared camera shots, which continue to be somewhat distracting. This is undoubtedly the point of the story where you know it’s going to be a long, hard slog to the finish line.

There are a few amusing moments though, such the continuing question as to why the Zarbi are frightened of a tiny (and very dead) spider. Barbara and the Menoptera’s attack on one of the venom guns is another notable incident – the high camera angle enables the actor under the costume to crawl away, which allows one of the Menoptera to pick up the empty shell and squish it against the wall, rather like one would deal with a bug.

You have to respect William Russell – an actor who never gave less than 100%. Even when surrounded by the Optera he ensures that Ian doesn’t for a moment give the audience the impression that this is all faintly ridiculous. It’s a difficult balancing act – with a less skilled actor, Ian would simply become po-faced and unbelievable – but Russell manages to ensure that Ian keeps his credibility at all times.

By far the most notable new arrival is that of Hilio (Martin Jarvis). Over the last fifty years or so he’s become one of Britain’s most distinctive actors, thanks to numerous film, stage, television and radio appearances. It’s hardly surprising that he’s not so recognisable here, but his familiar vocal tones are present and correct.

This wasn’t the easiest of episodes to navigate, but at least we’re four down with two to go.