The courtroom drama is pretty inevitable in any long-running series (for example, The Avengers had put Steed on trial for the murder of Cathy Gale six months earlier), and the early 1960s were a golden age for them following a string of high-profile trial moves, like 12 Angry Men, Witness for the Prosecution and To Kill a Mockingbird. So it’s not surprising to see Doctor Who jump on the bandwagon.

There’s a lot of commentary that says the Doctor only becomes the show’s leading man in Desperate Measures, when he unveils the truth behind Koquillion. But that’s not how his reappearance is played here: the start of the episode features the regulars wondering where he’s got to, and his return is treated as a big moment, acknowledging that the audience has been waiting on him. Ian, the central character of the last fortnight, is immediately relegated to secondary status following the Doctor’s reappearance. Similarly, the Doctor’s grand unveiling of the killer in Desperate Measures is almost a repeat of what he does here – within minutes of putting his mind to Ian’s predicament he’s worked out whodunit. ‘Elementary,’ he declares to Barbara and Susan, as he delights in his own cleverness. His grandstanding in court, and re-enactment of the murder place Hartnell right at the centre of the episode. The other characters, who a week before were ably carrying the show, are totally overshadowed. By May 1964 there’s no question Who is the leading man in this show. As if to confirm it, we even get – I think – the first ‘Doctor Who?’ joke:

Ian: Yes, I do know someone, if I can find him.

Tarron: Who is he?

Ian [laughing]: Who? He’s a doctor

Elsewhere, there’s a lot of nice attention to detail that suggests the wider world of Marinus, beyond these few rooms. Little references to being sent to the ‘glass factories in the desert’ are the kind of thing Robert Holmes throws into his scripts (e.g. ‘It sure beats picking chacaws’), and even George Lucas’s Star Wars films with their ‘spice mines of Kessel’. The detail extends to the set design, with the Archimandrite-hatted judges, like something from an Orthodox synod, and their weird swastika logo.

Sadly, the episode is a bit hobbled by Ayden’s stupidity when he twice blurts out his involvement in the theft of the key – although even that’s not too much of a problem when it results in him being assassinated to prevent him from revealing a wider conspiracy. Given rumours that Lee Harvey Oswald was killed before he could talk date back to December 1963, and the conspiracy theory Who Killed Kennedy? was published the month this episode was broadcast, it’s easy to see this as Nation riffing on current events.

Other things to note: it’s quite amusing seeing William Russell on trial for murder here in the knowledge of his son’s role in How to Get Away With Murder. This is the first episode in weeks that doesn’t feature a self-contained plot. The cliffhanger – a kidnapped Susan speaking on the phone with Barbara to tell her ‘They’re going to kill me’ before being abruptly cut off – is truly chilling.

Next episode: The Keys of Marinus