Fidel-Castrovalva is the first serial of the 19th season of Dog-tor Whoof (go away K-9. Bad dog). It stars Peter "Mustache" Davison in his first full story as the Irritatingly Reasonable Doctor alongside qt3.14 and Heathrow, while Adric, thank goodness, spends the whole story in Missy's sex chamber (I am not kidding).
It was written by Christopher H. Birdbrain and is the third in a Master trilogy that has a shit-ton to do with recursive mathematics, entropy, and holy shit I don't care (I say that as a fan of these episodes); the previous episodes in this trilogy are The Keeper of Krakens and Lipopolis. The newly regenerated Doctor is a fucking idiot for pretty much the entirety of the serial, but that's the trouble with regeneration- you never know what you're going to GODDAMN IT WHERE'S THE FUCKING ZERO ROOM?!?
Anyway, the Master captures Adric and creates a trap for the Fresh Prince of Gallifrey (aka Fivey). We don't know what this trap is until later because first the Master forces the TARDIS to go back in time to the Big Bang itself, because so evil much clever.
Meanwhile, the Doctor goes off his rocker, puts on a cricketers outfit, and finds a wheelchair so he can pretend to be Xavier from the X-man files. He then barges into the console room and tells Nyssa and Airport to jettison a quarter of the TARDIS because thrust (Birdbeak, in all his mathy-computery wisdom, has no concept of inertia- BRAVO BIRDMAN), but more likely because he got tired of the TARDIS' shit and wanted to show his waifu who's boss. We learn immediately that Fivey is pimp as hell.
Then Five gets comfy in a door-coffin while the girls do all the work to carry him to Castrate-vulva, where the Doctor is supposed to rest until he stops being an idiot (he doesn't). Somehow Nyssa and Tegan get split up from the Doctor, but then they don't, and they're all in Castle-valve-o together and people are happy.
But then the Doctor reads a bit too much, gets a stroke, and figures out the Master created Cast-a-vowel-eh? as a trap. The Doctor and his qt companions try to escape, but discover they're stuck in a recursion and can't get out (then they discover they're stuck in a recursion and can't get out (then they discover they're stuck in a recursion and can't get out)), so they find the Master and blow up his Adric-sex machine, unfortunately rescuing A-choo in the process.