Peter Davison’s debut as the Fifth Doctor owes much to Season 18 Script Editor Christopher H. Bidmead’s love of mathematics. When invited to replace the original Season 19 debut story with a new script, Bidmead would revisit certain ideas he had used in Tom Baker’s swan song Logopolis – in particular the concept of recursion, which in that story had manifested itself as a TARDIS within a TARDIS. For Castrovalva, Bidmead would put this concept on steroids.
Peter Davison’s first broadcast adventure was not actually his first recorded adventure – by this stage they had recorded Four to Doomsday, The Visitation, and Kinda. In practice this works extremely well, providing a TARDIS crew already well settled with one another, allowing them to pull off an ambitious regeneration story. Picking up directly from Logopolis (including a rare pre-title sequence film section reprising the regeneration) the TARDIS crew escape from the Pharos Project on earth to find the Doctor highly unstable – the first time in the show’s history it is overtly suggested that a regeneration can go wrong. The Doctor spends most of the adventure trying to find a peaceful space in which to recover while his regeneration completes – initially a room in the TARDIS known as the Zero Room, then latterly a dwelling of simplicity, the titular town of Castrovalva. Behind this story, very much in the theme of recursion, are layers of traps within traps, all set by the Master.
Kindapping and then releasing Adric at the very start of the adventure, the Master impels Adric to send the TARDIS directly into a supernova. In the truest style of the Hooded Claw, the Master then lays a trap within a trap – the town of Castrovalva itself. Leaving information about the fictional town in the TARDIS databanks, the Master uses Adric’s mathematical genius to use a skill revealed in the previous adventure of Logopolis – the capacity to build matter through pure mathematics. Adric constructs the entire town as a trap for the remaining TARDIS crew, and the Master lies in wait (disguised, obviously!) for the right moment to strike.
The more thoughtful reader might conclude with some justification that the entire plot is needlessly complicated – but to write off the story on these grounds would be to miss the enjoyment of the story. In rather the same way that The Edge of Destruction was crucial for building the relationship of the initial TARDIS crew of Season 1, Castrovalva really allows the viewer to get a better flavour for how Nyssa and Tegan would relate to the new Doctor; unfortunately for Adric, he spends most of the episode imprisoned by the Master, perhaps foretelling the rather grim destiny the producers had in mind for him. While the inspiration for the story is undoubtedly mathematical (making this story one of my dad’s favourites) it is not so overtly mathematical that it is impossible for the less mathematically minded (viz. me!) to follow!
Davison himself plays his role superbly – there is a wonderful moment in episode 1 in which he appears to regress to the mannerisms of the First and Second Doctors – very well acted, and an utterly charming nod to the show’s heritage. As debut stories go, Castrovalva is one of the very best, and a very pleasing conclusion to the ‘New Beginnings’ trilogy. Perhaps because it borrows so heavily from themes in Logopolis, it is harder to imagine this story working so well as a standalone adventure. The fact that it nevertheless does, is very much to its credit!