Roots: The work of Charles Dickens, particularly Oliver Twist and The Signal-Man, plus other works (the Doctor describes Creek's emporium as "a very Old Curiosity Shop" and quotes from A Christmas Carol "[Phantoms] wandering hither and thither in restless haste..."), Pickens may be a play on Dickens and The Pickwick Papers. Henry James' The Turn of the Screw plus the short stories of M R James. Baker Street is via Conan Doyle's Sherlock Holmes stories and befits the 'detective' chapter of the story (it's possible that Robert McIntosh, a student doctor at Edinburgh college of medicine, is an analogue for Conan Doyle). The Woman in Black. Animal Farm ("In a quantum universe all futures are possible, but some are more probable than others.") John 11:25 "I am the resurrection and the life saith the Lord", Matthew 5:5 "Blessed are the meek" and Exodus 20:13 "Thou shalt not kill." Aladdin's cave. The use of the term 'Bootstrap paradox' alluded to but not used explicitly for the time-travel paradox was popularized by Robert A. Heinlein's story By His Bootstraps. The Doctor's time at the Royal Academy refers to James Maxwell (a "good friend") and Léon Foucault.
Technobabble: The Doctor tells her that if you make certain adjustments to an electromagnetic field generator, it becomes a surprisingly good field interface stabiliser.
Using contemporary components the Doctor creates a Vortex Interferometer (which pretty much does what it says on the hypothetical box).
Goofs: Nyssa's jump from train in episode two - can't be caught?
Davison's voice is pretty croaky in episode 4
Why does Brewster's mother sing Oranges & Lemons anyway?
Dialogue Triumphs: "Doctor, landing a TARDIS inside another TARDIS is dangerous enough without it being the same TARDIS at an earlier point in its history" "-Really? I thought it was rather neat!"
"That's the problem with power cuts, they always happen when the lights go out"
"This fog can be murder for a young girl"
The Doctor on Victorian London: "I've been careful to tell them things they already know, I think that's why they like me."
"My stomach is not at its usual address"
Continuity: Thomas Brewster is in his early twenties (his birth year is somewhere around 1846/7, while his earliest memory is of his mother's funeral in 1851 when he 'must have been about four or five.') A housemaid, Brewster's mother committed suicide by jumping off Southwark Bridge in despair at raising the boy alone (though she did love him, apparently), and Brewster was sent to a workhouse, the 'Spike' by his extended family. After having been at the workhouse for ten years under the unsympathetic and brutal Mr Shanks he is introduced to a man called Creek and an apprenticeship as a 'river-man' (in actuality a mudlark). After fleeing Creek's death by misadventure with his friend Pickins in 1865 Brewster became a petty thief; his lodgings are "somewhere under Portland Road."
Although only a very remote possibility, a potential future Earth in 2008 is as a burned-out world dominated by phantoms or 'death-wraiths', beings of some psychic potential and composed of suspended gas particles. Aware of other potential realities viable for control they have sent a psychic projection from their reality into Brewster's present - back into the past - via a time corridor to influence events and make their version of the future more likely The Doctor theorises that such an effort would require an astronomical amount of energy to communicate through time, hence their alternative Earth of 2008 is burned out with the energy required. When he arrives there, Brewster, as the locus of the phantoms' influence, experiences near-fatal neurological trauma as a proximity side-effect of being too close to the source of the link.
Nyssa has a TARDIS key in her left breast pocket (although Brewster steals this.)
During a power cut the Doctor and Nyssa explore the lower floors of the TARDIS, finding a wine cellar (see: Untelevised Adventures), the Ship's conceptual geometer and the nearby ancillary power station. The geometer's Vortex shield relays are damaged, while The TARDIS' own field interface stabiliser has apparently seen better days.
After the time breach, the Doctor is able to restore enough power in the TARDIS for an emergency materialisation, arriving in London twelve months before present events. During the year waiting for Nyssa's arrival, he and the TARDIS have been lodged at 107 Baker Street, while the Time Lord has gone under the name of Dr Walters, grown a beard (people weren't taking him seriously due to his youthful appearance), and taken a new 'assistant' in Dr Robert McIntosh (though the two have not shared any particularly adventurous escapades.) In order to gain access to the materials he needed to repair the Ship (including an electromagnetic field generator 'borrowed' from James Maxwell), the Doctor has become a member of the Royal Society and has become involved in other gentlemanly pursuits. He regrets that he seems to have a habit of losing good friends and carries a spare TARDIS key.
Links: The Evil of the Daleks (time travel using mirrors and lenses). The TARDIS creates a breeze as it materialises (Doctor Who) "Ash and clinker" as the destiny of Earth (The Mutants)
Untelevised Adventures: In the TARDIS wine cellar is a Madeira, the property of Benjamin Franklin, 1784 (he would have been in Paris)
Location: London, November 14th 1867
The Bottom Line: "I was with you as far as 'bootstraps'"
A little bit fussy - the further adventures of the TARDIS in Brewster's early life might go some way to explaining some of his visions, but overcomplicate a story already brimming with coincidences and red herrings. In all, a bit clever-clever, but there's some welcome humour with the Doctor and Nyssa, and it would have been nice if Robert had been able to stay around instead of being yet another convenient sacrifice. Despite a great soundscape the incidental music is the real haunting terror though - a frequent earworm hasn't been this unwelcome since Something Inside.
Thomas Brewster's spectral 'mother' isn't the only identity guilty of creating a 'bootstrap paradox' in this story; the Doctor, trapped when Brewster steals his TARDIS, does much the same. Brewster steals the TARDIS under the instruction of his 'mother' in 1867, piloting it to the alternative 2008 where, overcome with psychic sickness due to his proximity to the source of the phantoms' signal, he collapses. Meanwhile, back in London Nyssa recalls Brewster recognising the Police Box from Creek's shop, and she and the Doctor go there to find the Ship still in situ, two years on from when Brewster and Pickens recovered it and fled Jacob's Island. Checking the TARDIS flight log the Doctor returns to the earliest of two most recent and unfamiliar destinations - 2008. There they materialise inside the TARDIS Brewster has stolen (the same ship at an earlier point in its history of course), rescue Brewster and programme the 'old' TARDIS back to the second unfamiliar destination, the bottom of the Thames, 1833 - an arbitrary date, all things considered, and only chosen because it had already been chosen in the TARDIS' past by the Doctor's present actions! The Ship lies at the bottom of the Thames for thirty-four years until being washed up in the mud somewhere near Jacob's Island, to be recovered by Brewster and Pickens and find its way into Creek's shop. In this way the Doctopr ensures his own rescue by 'programming' past phenomena from his own future. It's a good thing Nyssa's memory stored Brewster's own recollection of seeing the TARDIS or it would have all come unstuck. As it happens the Doctor seems to be becoming adept at performing tricky TARDIS manoeuvres in this story, essentially performing a time ram on his own Ship, crossing his own time stream and risking the Blinovitch effect with the two Brewsters coming into close contact.