The Keys of Marinus (Episode 6)

The one where we discover a secret romance...

Ooh, it's one of those rare occasions where an episode has the same title as the overall serial. I think it only happens three other times (five times if you include An Unearthly Child and The Edge of Destruction - some people do, including the BBC!) - for Planet of Giants, The Web Planet and The Space Museum.

Anyway, we rejoin Barbara, Altos and Sabetha, who must try to rescue the kidnapped Susan while the Doctor focuses on releasing Ian. There's a wonderful moment where the trio announce they're going to go to Kala's house to question her, and in the very next shot, Fiona Walker is opening the door to Jacqueline Hill, who looks a little flustered to be in the next scene so quickly! Walker (who gives good value for money as the unhinged Lady Peinforte in Silver Nemesis) is fabulous as Kala, bringing all her Shakespearean experience to the fore. She feigns mourning at the loss of Aydan, but as soon as her visitors are gone, reveals her true duplicitous self, and goads the gagged Susan in the next room.

Sentence of Death (The Keys of Marinus Episode 5)

The one featuring assault, domestic violence, murder, robbery, kidnap, perjury and bribery...

This episode is one of those with a distinctly educational vibe to it, laden as it is with courtroom intrigue and lashings of law and order. The establishing scene sees Ian wrongly accused of murder and robbery, but in Millennius it seems the tables are turned in favour of the prosecution, because Ian now has to prove he didn't commit the crimes, rather than the other way around.

The children watching get a good grounding in how justice works as we're introduced to a tribunal of judges, cases for and against the accused, case history and some prime Holmesian deduction on behalf of the Doctor.

The Snows of Terror (The Keys of Marinus Episode 4)

The one where Vasor gets close to Barbara, and Ian gets close to Altos...

Gorgeous, operatic music accompanies the opening of The Snows of Terror, foreshadowing similar icy arias used in The Ice Warriors three years later. Ian and Barbara collapse through cold and tiredness, although Babs gets one last look at a big hairy man looming over her before she passes out completely. Is she too tired, or is the vision of masculinity before her just too much to cope with? Vasor isn't her usual type...

This is the episode of The Keys of Marinus which has always fascinated me most. It's the character of Vasor that gives me food for thought because he's a curious chap. While on the surface he might seem a very simple character to define, when you actually look at his behaviour across the 25 minutes, he becomes one of the more nuanced characters in Terry Nation's early work.

The Screaming Jungle (The Keys of Marinus Episode 3)

The one with the screaming jungle that whispers...

Susan was the most unlikely adventurer, wasn't she? I know she was only a teenager, but she was a teenager with quite a lot of intergalactic adventure under her belt, but still she goes to pieces at the slightest hint of danger. Experience has not jaded her, or even toughened her up. She's the biggest wimp the Doctor ever travelled with.

She can't even calm down enough from her hysterical fit to explain to Ian and Barbara what's bugging her. "It was... it was... it was horrible!" is the best she can muster. She needs one of those slaps that burly heroes give to hysterical maidens in all those old films when they can't calm them down, except slapping people across the face isn't really what Doctor Who does. Not until Russell T Davies gets hold of it anyway...

The Velvet Web (The Keys of Marinus Episode 2)

The one where everything is much grimmer than it seems...

It transpires that the blood Ian found on Barbara's discarded travel dial was just a scratch on her wrist, and she's actually perfectly safe and lording it up in what appears to be an intergalactic version of Ancient Rome (echoes of the future here...!). The Doctor, Ian and Susan find Babs reclining leisurely on a chaise longue, quaffing orange juice and popping grapes as if she's been there for days. From the others' perspective, it's been a matter of mere moments, but perhaps Barbara's travel dial took her back in time somehow? Or maybe writer Terry Nation just didn't think it through very well.

John Gorrie's direction in The Velvet Web is a real step up from last week's shambles, and the effect when the Doctor, Ian and Susan break through the doors into the city of Morphoton is well-handled, with flashing white lights and disorientating sound effects. The way he handles the problem of swapping perspectives once the truth of Morphoton is revealed is excellent, so subtle at first, flipping between Barbara's view of a society in ruins, and the others seeing pomp and finery. The viewer notices the differences gradually, making it an experience for us as much as those on the screen.

The Sea of Death (The Keys of Marinus Episode 1)

The one where Susan is terrified by the loss of a shoe...

After 20 weeks of the viewers getting to know Doctor Who and his band of intrepid space and time adventurers - and those characters getting to know one another too - it's almost like the production team has hit the reset button, as The Sea of Death opens afresh with no connection to previous adventures apart from Ian's Marco Polo shirt.

But hold on, not everything feels fresh. The Sea of Death is written by Terry Nation, in one of only two instances when he wrote a non-Dalek Doctor Who story (the other being 1975's The Android Invasion). And there's a lot in this episode which echoes his work on The Daleks just a few months earlier...