Roots: Monty Python and the Holy Grail, Jabberwocky, Spamalot, The Black Adder. The fictional district of Mummerset, a portmanteau of 'mummer' and 'Somerset', is named after a stage dialect supposed to represent a generic West Counties accent. The Doctor quotes from Percy Shelley's The Castle and compares Hubert to Wat Tyler. The Mummers' play appropriates of elements of the 'Bold Egg Play' and Saint George legend (fittingly, also a non-Briton), while Roland of Burgundy openly capitalises on the legend of Childe Roland. Viridios is indeed a 'green man' of European folklore. There's also a joke about Russell Brand in there, apparently.
Intertextuality: The Doctor refers to the Rutan's Sontaran quarry as "Jingo Linx", a full name which only appeared in Terrance Dicks' Target novelisation of The Time Warrior. The Rutans' description of the Sontarans as 'trolls' comes courtesy of Terrance Dicks' usual shorthand description of the Sontaran race.
Several Stockbridge comic strip elements and locations are alluded to, including the village, Wells Wood and Sir Justin (The Tides of Time), the Redfern Inn (Stars Fell on Stockbridge), the Green Dragon Inn (The Stockbridge Horror); 'Grubb' is presumably a forebear of J Grubb, proprietor of the general store in The Iron Legion (later ret-conned as being initially set in Stockbridge), while 'Maud the Withered' is apparently a forebear of Mrs Alice Withers (The Stockbridge Horror), or more correctly her husband - though given both Maud and Alice are played by the same actor perhaps banjo playing figures in the family history?
Technobabble: "I need to find some way to stabilise the sinus rhythm, otherwise the hyperspatial warp core will ignite and the entire ship will explode!!"
Goofs: Hubert offers a fortune in non-specific 'gold pieces' - in fact the only coin available in post-Norman Britain was the silver penny (no wonder he resorts to offering land)
Why put a waterwheel in a moat? Not only is it tactically and defensively reckless (especially on the outside of a castle wall), moats are for the most part stagnant water [perhaps the moat of Stockbridge castle is fed by an underground stream, or spring, or a river (not the Stock, as it's more than a mile to the east) hidden by the Rutan mist? Or maybe a wizard did it?] In fact, once the Rutans had enough clones, why not use their manpower to turn the wheel instead? And where did the clones' clothes, armour and weapons come from?
"It was twitching, like a decapitated limb" (assuming said limb once had a head of its very own)
Dialogue Disasters: Every mention of Maud - "What, Maud the strumpet?" "Nooo, Maud the Withered!" It was pitiful the first time!
Continuity: Stockbridge in this story is part of a larger county called Mummerset (see: Roots). Stockbridge Castle lies a couple of hundred yards from the edge of Wells Wood (presumably this is of greater size, also it is not said whether it is on the near or far side approximate to the village, although see The Eternal Summer for further detail) and includes a barbican or gate house, bailey wall and moat (see: Goofs) with a water wheel and (probably) running water, a high keep, and inside among its quarters a wine cellar and dungeons with a working rack. A secret tunnel leading below the moat and to the wine cellars can be found within a hollow oak in the Woods, over a thousand years old and bearing Roman graffiti, including the Romano-Greek phrase 'Veni, Vidi, Viridios'. The last Earl of Mummerset, a noted womaniser, left for the Crusades seven years previously and died in Palestine - the fate of his heir is said to have been due to a horrific head wound. New Stockbridge locations include the Turk's Head pub (1899) and the river Stock, which appears to have flowed through Wells Wood at least during the middle ages. The village has a working blacksmith's and an economy based on livestock and 'spreading mud'. Wells Wood, apparently the property of the Earl of Mummerset, is home to 'Mummerset blacks', voracious wild boars with great appetites. Fish swam in the river Stock until recently, having been all but wiped out on the arrival of the 'falling star' - the Rutan Ship, not long after the Earl's departure). The title of Earl of Mummerset becomes assumed by 'Hubert', aka George of St Albans, an apothecary's assistant who tended (unsuccessfully) the true heir to the earldom. He becomes the future 'Saint George' of the Stockbridge mummer's play, although his true fate and the possibility of any descendants are unknown. Presumably they are short-lived or nonexistent as the Doctor mentions the castle being nothing more than a ruin by the Twenty-first century.
The Rutans within the castle are part of a pursuit force seeking the Sontaran Linx (see: Links). Holed up in the castle while repairing their ship they have concealed its appearance by chameleonic technology mapping its coordinates with the outer dimensions of the castle's high keep. The crew comprise two Rutans, and the surrounding landscape has been transformed to suit the living needs of the Rutans, including a freezing 'pea-soup' mist and foul-smelling moss which grows everywhere except the illusory high keep. Rutan technology is currently exploring the potential of clone stock as cannon-fodder. This relies on a significant and constant power supply, hence the water wheel. Clone descendants may still retain some memories of their forebears though 'mimetic confluence', although these can remain dormant for centuries unless awoken.
Rutan ships are organic, at first gestating then growing over time - they can lie dormant for years until awoken by a Rutan or clone sufficient to answer their psychic call. Their control panels are crystalline and can have hexadecimal encryption and tamper-proof charges that would stop a human in their tracks (but not the Doctor). Their drives are metabionic, meaning that they are prone to 'get cranky' over time and fibrillate. Power is supplied by a warp core and energy lattice the Rutans' first ship makes use of the TARDIS' kinetic conversion unit [a dynamo?].
Nyssa refers to herself as Nyssa of Traken - it is unclear whether the Traken village mentioned in Circular Time: Autumn exists in 1199 (or 1899 come to that) - certainly none present appear to make the connection.
The Doctor says he hasn't visited Stockbridge before 1899 before now. He has not yet met Percy Shelley (see: Links)
Q.v. 'Sontarans and Rutans', 'The Sontaran-Rutan War'
Links: The Time Warrior. Nyssa and the Doctor refer to the events of their last visit to Stockbridge and Nyssa's liaison with 'Andrew' (Circular Time: Autumn)
The Doctor hasn't yet met Percy Shelley, but does in his eighth incarnation (The Company of Friends: Mary's Story). The Shakespeare Code ("I name you...")
Location: Stockbridge, including the Castle and Wells Wood, Boxing Day 1899 and 1199.
The Bottom Line: "This is ridiculous"
As described in advance by a post on Gallifrey Base: "On second thoughts, let's not go to the Castle of Fear. It is a silly place". Plot-wise it hangs together well enough, with some diverting twists. But it's as funny as being cornered at a party by a Monty Python nerd.
THE VILLAGE OF STOCKBRIDGE
Featuring in several audio stories, the Gloucester village of Stockbridge finds its origin in the pages of the DWM comic strip - or more accurately, Doctor Who Weekly, as the village has been an occasional location in the series since 1982. Indeed, the point of origin could now be earlier as the most recent Stockbridge story visually ret-cons the village geography to fit the hitherto unnamed setting of the opening of the Weekly's maiden Doctor Who strip The Iron Legion. For the most part however, the beginnings of Stockbridge proper are in the Fifth Doctor's era, particularly the loose trilogy comprising The Tides of Time (introducing the village and its green, Wells Wood and sometime companion Sir Justin after whom St Justinians Church is named), The Stars Fell on Stockbridge (in which first appear Maxwell Edison and the Redfern Inn) and The Stockbridge Horror (ditto Mrs Withers and the Green Dragon Inn). From The Iron Legion itself we have J Grubb's General Store, an inclusion referenced in most of Big Finish's Stockbridge stories, confirming the hypothesis that many fans have followed over the years, that the villages of Legion through to Alan Barnes' Eighth Doctor strip debut End Game are indeed the same. End Game's greatest contribution was in introducing Stockbridge's only true TARDIS companion Izzy Sinclair, who is realised in The Company of Friends: Izzy's Story and is also probably referenced post-mortem in Plague of the Daleks. As far as contributing to the village's character, the Stockbridge Trilogy and Izzy's Story add little here and there - a neighbouring village in Ashnorton, some castle ruins and the easily-inferred river Stock, for example.
What is more interesting is the first 'Stockbridge' story, Circular Time: Autumn which puts the Fifth Doctor and Nyssa in a very similar village given the same name, cricket ground and nearby woods where the TARDIS is situated (as it did during the comic strip cycle). Problematically, the story's village is located in Hampshire, boasts non-West Country accents (antagonist 'Don' is an import from Lancashire) and coyly refrains from tipping its hat to the usually-named landmarks, although one could easily accommodate the village as the genuine article (it even has the Doctor staying in a bed and breakfast run by a woman as in Stockbridge Horror) if we dismiss the Hampshire setting as an accident of detail (its writer Paul Cornell did much the same in his New Adventure Timewyrm: Revelation, setting it adjacent to his Cheldon Bonniface, Norfolk). In-story, the easiest solution is to assume the village is the same, as Nyssa's arrival in the village in Castle of Fear treats this very much as her return to a familiar location - the self-same Stockbridge.