Terror of the Vervoids146 does something of a first for the show (well, "An Unearthly Child" excepted): it introduces a companion in media res, without any of the "getting to know you" stuff that's usually standard for these things. This is of course because this story takes place in the Doctor's personal future (so, er, he's found innocent at the trial, then -- and when did this thing become a trial anyway? It started as an inquiry...), and so from his point of view he's already known Mel, the new companion, for some time. And so Bonnie Langford is introduced as something of a health nut, trying to get the sixth Doctor into better shape. Mel is somewhat relentlessly cheerful and bubbly, but as it makes a welcome change from Peri and the Doctor's more fractious relationship (even allowing for the softening we saw in the first two stories this season) the positives outweigh the drawbacks. (And, being American, I have no preconceived notions about Bonnie Langford going into this -- I understand that's not the case for the majority of British viewers.)
The actual storyline concerns a murder mystery, and other than a couple instances where the Doctor contests what's being shown in the courtroom, contending that it's been altered since he reviewed it in preparation, the trial interruptions are generally kept to a minimum -- thus allowing Terror of the Vervoids to develop its own pace -- and as this is intended to evoke Agatha Christie's stories, pace is a crucial concern. But it's an odd sort of murder mystery that Pip & Jane Baker are presenting us with -- the initial death turns out to have been faked, but then that person dies for real, while there's some stuff involving giant plants that seems to worry Professor Lasky and her two assistants (probably because they end up being killer plants). This means that the first mystery has been cleared up, the second leaves us none the wiser, and meanwhile there are a bunch of homicidal plants on the loose that nonetheless no one seems to know about, even though they've started killing people too. It's almost like setting Murder on the Orient Express (and note the homage early in part nine) in the middle of a slasher movie. And since this is a Pip & Jane Baker script, people talk in ludicrous ways; infamously, Michael Craig, as Commodore Travers, has to deliver the line "Accident? Why can't you use plain language, mister?" and then follow it up with "Whoever's been dumped in there has been pulverised into fragments and sent floating in space, and in my book that's murder." He also gets lines like, "I should accept that advice and drop the sophistry", while the Doctor has to say things like "The weird atmosphere down there could lead to phantasmagoria." It's particularly obvious with Craig because he spends the rest of his time trying to play a no-nonsense ship commander, and the dialogue gets in the way of that.
Nice design though; you do get the sense that this is a luxury liner (the cabins in particular seem to have been designed to be small and claustrophobic, as you'd expect), with carpet on the walls and warm colors everywhere. Plus full marks to whoever decided to put framed comic book pages up as artwork in the cabins. And there's a nice costuming touch that's been going on throughout the season: Colin Baker's cravat changes color (so blue means past, red means present, and now yellow means future) to act as a subtle indication of what version of the Doctor we're watching.
So it's not the worst thing ever, but judgement of Terror of the Vervoids will probably depend on how it resolves the various problems and mysteries it's setting up. Nice cliffhanger into part eleven, though; the design of the mutant is realized very well.
146 As the whole season is officially called The Trial of a Time Lord, we get to hark back to the days of William Hartnell and debate what to call these segments. The first two had their accepted titles on the scripts, so no problems there, but the working title for this third segment was first The Ultimate Foe (now the accepted title for the last two parts -- a confusion that might have occurred because these last six episodes share a production code of 7C) and then The Vervoids. Terror of the Vervoids is a title that was invented for the Target novelization (although it's not clear if it was someone at Target or Pip & Jane Baker who actually came up with the title) and which has since stuck with everyone except the people who insist on referring to The Daleks as The Mutants.