Roots: The Land That Time Forgot, The Lost World, The Scorpion King, The Incredible Shrinking Man/King Kong (giant spiders). Rupert begins to recite the Lord's Prayer.
Intertextuality: The Doctor likens Brewster to Adric, closing the 'Artful Dodger' link in the original character biography of Adric.
Double Entendres: "I've experienced the most terrible things - like the time I was taken up the Limpopo by the natives."
Dialogue Triumphs: "She's bargaining with the one remaining thing she can" "-You mean... her 'honour'? Bally hell, that's a rum situation!"
Technobabble: The Doctor theorises that Adric must have a telepathic frequency enhancer, like a sort of psychic magnifying glass.
Continuity: Separated from the TARDIS, the Doctor and Nyssa have met Bernice in a tea-shop near the British Museum, where she overheard them discussing the fifth dimension. Enlisting her aid with that of the twelve-strong members of the Bloomsbury Circle, the Doctor has adapted a 'séance' into a concentrated experiment in block transfer computation to seek out a trace of the TARDIS' probable location left in the space-time continuum. During the séance two things take place which bring about the real fate of Adric and reunite him with the Doctor. In the first instance the Time Lord's guilt causes him to take a 'detour' into his past, causing an apparition of him to appear on the bridge of the doomed space freighter, feeding some of the computations into the mind of Adric unawares. The revised computations steer the freighter away from its apparent course and into the second consequence of the Doctor's computations, a time bubble where he and the surviving members of the Circle eventually also find their way.
Five hundred years have passed since the crash of the freighter, during which time Adric (who survived the crash due to the Doctor's subconscious intervention) has increased his natural affinity with arachnid creatures to communicate with the native life forms using Star, and train them in block transfer computation, sustaining the time bubble separating the City of Excellence from the rest of the planet and extending his life with it. The dominant life form therefore is that of Arachnidae - scorpions, spiders and also insects in the form of 14-foot high mantids and the termites of the City. Dinosaurs have never appeared in this particular bubble of reality, their proto-reptilian ancestors having already been devoured by the arachnids. When the constant computations of the City's population ceases and Star's influence is removed, the bubble collapses.
The foundations of the termite mound City of Excellence are formed from the infrastructure of the crashed Cyberman freighter (its cyborg crew have been devoured by the scorpions) with bridges formed from spider silk. 'Star' is the alien computer (an 'untutored artificial intelligence') that was controlling the freighter on its journey to Earth - the Doctor likens it to a crystal brain.
Six weeks pass in real time since the Doctor and Nyssa disappear and, presumably since Brewster's stealing of the TARDIS. During this time Brewster has piloted the machine alone, but with near-disastrous consequences, coming closer to crashing into the temporal horizon but for Adric's intervention.
Nyssa deduces that the TARDIS isn't in this time period, because if it was it would be telepathically translating their words. She knows that block transfer computation doesn't work instantaneously.
The Doctor senses "the particles in the air being shunted around, as if making space for something" as the TARDIS materialises.
Location: A time bubble modelled on prehistoric Earth (possibly Central America, given the preponderance of podocarp vegetation and the likely crash site of the Cyber freighter), circa 420 million years before present and nearly five hundred years after the crash of the freighter.
Links: Earthshock, Time Flight, The Haunting of Thomas Brewster. The Doctor says "Brave heart... Beatrice". Adric's names for some of the scorpions are of course relative to his time with the Doctor - Kranlee [Black Orchid], and Teegarna the 'mouth on legs'. Logopolis (block transfer computation, the City is modelled on the planet, and Adric refers to the Doctor's fatal fall). The Doctor mentions Iris Wildthyme (who he will later meet whilst travelling with Nyssa and Tegan - Excelis Dawns). Adric's affinity for arachnids may be a reference to the marsh spiders of Full Circle.
The Bottom Line: "Bit of number trouble, Adric?"
Oh dear God. Despite some fun to be had with the Bloomsbury Circle in prehistoric Earth, this will be remembered as a reworking of Earthshock's hardware and finale resulting in a sequel that surely nobody anticipated, nor asked for. The recasting of the mathematical genius seems in retrospect a necessary ruse, but aside from Andrew Sach's rather good performance this just comes across as ultimately another boot to kick the companion's legacy with. Despite its redemption for the character (who nevertheless is made 'bad' for the purpose), this is ill-advised in concept and execution, and thankfully as bad as Big Finish's output gets.