Roots: Professor Challenger and Sherlock Holmes stories, particularly Hound of the Baskervilles.
Goofs: Some details of Arthur Conan Doyle's life have been changed.
On page 64, Lucy was kidnapped almost two years ago, though it is stated several times elsewhere that the kidnapping of children began 12 months ago.
Technobabble: What exactly is a semi-opposable thumb? Surely a thumb is either opposable or not.
Dialogue Disasters: Arthur Conan Doyle: 'I think it's dashed irregular to use young urchins as agents.'
Dialogue Triumphs: Sarah on the TARDIS swimming pool: 'That's a Bathroom?'
The Doctor: 'Yes. Can't you see the rubber duck in the tub?'
The Doctor: 'I was lost in my thoughts. I have so many, it's easy to get lost.'
Sarah: 'You mean you could really control the TARDIS if you want to?'
The Doctor: 'Only when it's very important.'
The Doctor: 'When have I ever let you down?'
Sarah: 'Too many times.'
The Doctor: 'That was in the past. And we've definitely passed through those times.'
Sarah: 'Are you absolutely certain this is India?'
The Doctor: 'Absolutely.'
Sarah: 'Then it's probably the Isle of Ely. Or another weird alien planet.'
Kipling: 'What are you a Doctor of?'
The Doctor: 'This and that. That and this. Mostly that.'
Alice: 'I don't know if you know anyone.'
The Doctor: 'I know a lot of people, though I doubt if any of them are here.'
Alice: 'A death? Is it ...?'
Footman: 'One of the villagers, my lady. No one important.'
The Doctor: 'Has it never occurred to you that the human understanding of science is a small and pitiful thing? That there might exist vast areas outside of human knowledge that can still be explained scientifically, but not in terms of the puny knowledge that the human race possesses at this time? That there just might be realities undescribed by and unknown to your limited grasp of science?'
The Doctor: 'Sarah never does what she's told. She's almost as bad as me in that respect.'
The Doctor: 'I can see that you're a busy man, things to do, worlds to conquer, infinitives to split and all that.'
Sarah: 'You can't change history.'
Beckinridge: 'Your history, Miss Smith, not mine.'
Continuity: The Doctor carries a magnifying glass and can ride a horse very well. He speaks fluent dolphin. Sarah is good with a gun, and can ride. Zoe used to have a low-cut bathing suit, which she left in the TARDIS. Sarah has done a little sailing, but is otherwise unfamiliar with boats.
Queen Victoria has a secret agents who investigate things that are out of the ordinary [presumably these were the earliest incarnation of Torchwood - see Tooth and Claw].
Rutan healing salve figures out what's wrong with a Rutan and heals it. It can heal wounds in humans, assuming that there's no infection from other DNA. If there is DNA from two or more species, it can combine the two. It has no effect on Time Lords.
Links: We see the TARDIS bathroom/swimming pool (The Invasion of Time). There are references to events in The Brain of Morbius. Sarah's bedroom appears to have previously belonged to Victoria and Zoe. The Doctor mentions Metebelis (Planet of the Spiders) and Argolis (The Leisure Hive). Sarah recalls her encounter with Sutekh ([TV]Pyramids of Mars[/FP]) and her first trip in the TARDIS (The Time Warrior). The Doctor uses his UNIT pass.
Location: Dartmoor, 1880 (page 6), a week before term starts (page 84).
Unrecorded Adventures: The Doctor had a TARDIS manual, but he can't remember where it was, or which incarnation lost it. He thinks he may have met Arthur Conan Doyle before. He also claims that he has, on occasion, worked with Scotland Yard [perhaps he's referring to UNIT].
The Bottom Line: A well-plotted tale with very few loose ends. There are lots of absolutely excellent lines, and the whole thing holds together pretty well. It is also well set in its historical period. Not a stunning example of Doctor Who, but far better than its reputation.