Roots: Braveheart, Rob Roy (whom the Doctor compares to Robin Hood), Scottish and border folklore (particularly legends of the Redcap, Shellycoat and kelpie, while Jamie compares a siren to the Irish 'banshee') The Doctor paraphrases Ghandi's turn on the biblical phrase "an eye for an eye" ("... til we all go blind") Jerusalem ("dark satanic mills") Mornington Crescent. Casablanca ("I think this could be the beginning of a beautiful friendship") 'Black Donald' is a colloquial epithet for the Devil in Highland Scots lore. Yankee Doodle Dandy
Dialogue Triumphs: "Providence, eh? That's a strange name for a lassie."
"There's always time - if you know where to look!"
Double Entendres: "Who's your friend, Donald? He looks like some Yankee Doodle!"
"Don't say you're scared of a few little bangs?"
Continuity: The Doctor surmises that the strange anachronistic elements of the landscape and battles is due to "temporal foldback distortion", although this doesn't account for Jamie not knowing the Doctor at all (again, he should have a "small memory" of their time together from The Highlanders.) The people bleed red (likely a narrative necessity to fit the inclusion of the Redcaps.) Locations mentioned include Kelpie's Flow, Lammermoor Estate, Grangemouth (the titular city with monorails and skyscrapers, all within a great glass dome) and the Great Maw, an open cast iron mine.
The Hirudin Conglomerate is known throughout the Four galaxies (although the Doctor hasn't heard of them), having been beset by "heroes" attacking their various corporate divisions. They are alien bloodsucking leeches who share gestalt intelligence, swarming and living parasitically off their hosts whom they cover from head to foot, and ultimately killing them in the process. Their servants, the 'Redcaps' appear to be some form of cyborg, created by the 'capping' procedure wherein a victim is injected with 'black water', a viscous and noxious fluid drilled like oil (as the Doctor initially thinks it to be) from the land and refined at Grangemouth.
Jamie appears here to be twenty to thirty years older than when the Doctor last saw him (it is not explained whether he is referring to the events of The War Games or The Two Doctors) - the Doctor thought him dead after they parted company.
According to the Doctor the TARDIS lock has "an advanced meson recognition system."
The Doctor says he's "not that sort" of doctor. He says he hasn't smelled air as fresh as this "for a long time". He has been following "a strange algorithm" picked up by the TARDIS. He thumps his chest to restart his second heart after being submerged in the 'black water.'
Q.v. 'The Doctor's Doctorate', 'The TARDIS Lock'
Links: The Highlanders, The Moonbase (Jamie's 'Phantom Piper'), mention is also made of "sailor Ben and beanpole Polly". The War Games. Rose (The Doctor's line referring to "the assembled hordes of Genghis Khan" and the TARDIS is similarly invoked.) More of the nature of the 'black water' is revealed in The Wreck of the Titan, while that of the Hirudin creatures is revealed in Legend of the Cybermen.
Mention by Guthrie of a 'sorceror' and his crooked-headed maidservant at Lammoor is a link to the Companion Chronicle Night's Black Agents by Marty Ross, set between this story and The Wreck of the Titan and telling of another Highland diversion met by the Doctor and Jamie on their way to retrieving the TARDIS.
Untelevised Adventures: The Doctor says he has 'stood on the brink of the Great Canyon of Mars."
Location: The Land of Fiction (though the Doctor thinks it 1780 initially, then 1884 while he is in Grangemouth)
The Bottom Line: "It's hard these days to tell men from puppets."
Lovely music, and a nice, affirming return for Jamie to the Doctor who, it's nice to note, seems genuinely eager to re-establish their friendship. Once the quasi-historical elements fall away, however, things become less interesting as the intrigue is piled on with ever more visual demands: cities of refineries, leech-people and the mysterious 'black water' among them. In the end, it's the Time Lord and his companion who provide the most interest, with the supporting cast either vague ciphers or vague allies. A strange beginning to what will, assuredly, become a more fantastic trilogy