To begin with the pairing of Peter Davison’s Doctor and Nyssa; as combinations of Doctor and companions go, it’s not the most exciting, given that the characters are just slightly too similar and there’s next to no tension between them. Davison works best with characters who bring out his subtly devastating line in irony, while Nyssa’s intelligence and innocence need a contrast. So Stephen Cole does the sensible thing and splits them up. Pairing the Doctor up with the sharp-tongued Monica (surely a nod to Friends) gives Davison something to play off and the Nyssa-Tulung pairing contrasts science and reason with spirituality and tradition. With such a small cast (five supporting actors in addition to Davison and Sutton) these pairings stay together for pretty much most of the story; it’s hard not to imagine that perhaps in deliberate contrast to ‘Whispers of Terror’, although we have a small group of people in an isolated setting, the story resists the temptation to bump them off one by one and instead creates a more mobile narrative in which characters move around freely. It’s disappointing that Shaun Brett never quite becomes a three-dimensional character given his family’s role in the backstory, but otherwise Lucy Campbell’s Monica is by far the most memorable character.

This is also the first of the Big Finish range to make a serious stab at monsters, and in the Permians Cole creates a race ambitious enough to be effectively unrealisable on television and with a sufficiently sound rationale to work in the audio format. In fact, the basic concept could almost have been intentionally designed to be unrealisable on television- a creature of bones, capable of absorbing characteristics from its victims and held together by its own bio-electric field. 1960s Who would have tried bravely but failed; 1970s Who would have had a line put through at the first stage by Terrance Dicks or Robert Holmes, and 1980s Who would have rejected the idea in favour of something which could emit gunge from various orifices when killed, but even in the CGI age the Permians could only have been realised with an obvious special effect. There’s also something distinctly unsettling in the idea of a forgotten evolutionary blind alley coming back to life which, combined with the way that the Permians are never really described in detail or illustrated, leaves the detail in the best possible place- the listener’s imagination.

If the story has a weakness, it’s probably in being a comparatively small-scale production with a limited supporting cast, not all of whom can be said to shine. Although the opening chords of the incidental music are perfect, the attempts at creating atmosphere aren’t all that successful and while the Cluedo-style plan of the monument is a nice gimmick, it’s also a tacit admission that the production itself fails to put over a real sense of the location where everything is taking place. But for all its limitations, there’s a sense of ambition here which makes up for the restrictions on the production, as well as a genuine sense of an attempt to use the audio format and incorporate some original ideas and as a result comes across as the most intelligent entry in the series so far.