First broadcast 11 January 1982.

The Doctor (Peter Davison), Tegan (Janet Fielding), and Nyssa (Sarah Sutton) finally arrive at the mountainside village of Castrovalva – but there’s something amiss about the community that lives there. And where is Adric (Matthew Waterhouse)?

After two episodes confined to the TARDIS, “Castrovalva” finally reaches its namesake, and it is honestly like an entirely new serial. Characters have more interesting things to do here, Peter Davison gets much stronger material to play, and the designers have a field day.

There are two elements I adore about “Castrovalva”, and both come into play in this episode. The first is that the episode finally expands to feature a proper supporting cast, and it is a classic ensemble of BBC regulars playing each of their roles with conviction and a wonderful sort of dignity. Derek Waring plays Shardovan, a somewhat suspicious librarian and academic. Michael Sheard, one of the most perennial of all Doctor Who guest stars, plays the physician Mergrave. Frank Wylie makes the most of a minor role as the gatekeeper Ruther. The only let-down is the village elder the Portreeve, who even from the outset is very clearly Anthony Ainley’s Master in disguise. Writer Christopher Bidmead’s dialogue shines here, with some risible lines in the previous episodes making way for something much more formal and old-fashioned. Each guest character feels real and likeable, and the only downside is a very 20th century lack of female characters. There is a little pack of washer-women, but they are all extras.

The other highlight is the design. Both the costuming and the architecture, the latter inspired by M.C. Escher’s artwork “Castrovalva”, really bring a sense of place to the environment. It feels like a real solid place, and what is more it all looks unified and interesting. It is a clever set, shot carefully by director Fiona Cumming from different angles to make one room look like an entire town of marketplaces and alleyways.

I am always conscious of Matthew Waterhouse’s acting as Adric – he was very young – so I feel compelled to note he is actually very decent here in his scene with Nyssa. He captures the right sense of drama here. Peter Davison is also very good here, playing out the recovery of an amnesiac Doctor with charm.

It is rare to see the quality of a Doctor Who serial lift so palpably between episodes. “Castrovalva” really is a story made up of two halves, and it is nice to have made it into the better one.