Big Finish have returned to an old theme in Who: the search for the Key to Time, as originally carried out by the Fourth Doctor and his Time Lady companion Romana in 1978.

The story starts with a Doctor-less narrative, The Prisoner’s Dilemma, with Ace, the Seventh Doctor’s companion, sharing a prison cell with the mysterious Zara, who is on a quest. I was not impressed, for much the same reasons as Rob Buckley. The plot resolution didn’t make a lot of sense to me (apparently an irreversible brain wipe is not irreversible after all), and Sophie Aldred’s weaknesses as a performer seemed to me cruelly exposed – Laura Doddington as Zara is better, but unfortunately this is not saying much. Can safely be skipped if you want to enjoy the other Key 2 Time stories.

I enjoyed The Judgement of Isskar rather more. First off we have Amy, the new companion and Key-to-Time-segment-trace-in-human-form. Ciara Janson, though very young for a Doctor Who audio companion, is really pretty good in this rather unusual role. On top of that, we have the Key to Time itself, Amy’s evil twin Zara plus sidekick, the early history of the Ice Warriors, and a rather odd insect-like culture, whose set-up frankly is total nonsense but the actors carried it off well. Peter Davison, who has now been doing the Doctor for 28 years, still seems to be in good form.

While The Judgement of Isskar was decent fare, I really enjoyed the latest BF, The Destroyer of Delights. Most of it is set in ninth-century Sudan, at the height of the Islamic caliphate. This is a potentially uneasy setting – Big Finish screwed up with a sensitive historical setting in The Marian Conspiracy, though did rather better with The Settling. This is more on the laughs side (Arabian Nights) than the didactic side, but both elements are there, and in my opinion it works.

It works also because of the cast. Ciara Janson again is good as Amy, backed by comedienne Jess Robinson as slave girl Nesrin; and Will Barton, who played Midge in Survival, gets to show off his fluent Farsi (not very accurate for the Sudan, but few will worry about that). But most of all, we have Peter Davison and David Troughton as the Doctor and the Black Guardian – not exactly a reprise of Daker v Buzzard in A Very Peculiar Practice (though I harboured a secret hope for an appearance by the High Priest Soldeed from The Horns of Nimon) but in one scene in particular gloriously picking up on each other. Each of them also gets some separately very funny moments: Davison with an exchange about the way in which “blue man” actually means “black man”, except, er, when it doesn’t; and Troughton in a brilliant gag from Oscar Wilde. Troughton also gets Jason Watkins, playing the White Guardian, to argue with.

Indeed, one of the other successes of the play is that it takes the concept of the Guardians and goes somewhere completely new with them, really cutting them down to size. And I must say I cheered. There are a few too many beings or entities with ultimate power over all life and matter in the Whoniverse, and it’s good to see that writers can demote them as well as create them. So, Destroyer of Delights is my favourite BF release this year. Admittedly, that’s from a field of, er, two.

This also marks the moment when I have actually listened to every single one of the 118 Big Finish regular releases to date. I’m not going to do a big assessment post now – that can wait until the tenth anniversary of The Sirens of Time in a few months, and in the meantime I can catch up with the other BFs I haven’t otherwise got to. I’ll just say, listen to The Kingmaker and also Spare Parts (both starring Davison’s Doctor, but at opposite ends of the emotional spectrum) and that will probably decide whether Big Finish is for you.