The search for the fourth segment of the Key to Time brings the Doctor, Romana and K9 into the shadowy world of Shangai gangs and the side-effect of a disastrous experiment in the far future.
Romana I and K9.
Pg 22 On the walkway of a bridge, Shanghai, 1937.
Pg 44 The TARDIS skips forward to dusk but remains in the same place.
Pg 284 In the temple in T'ai Shan, in the Shangdong province.
This is a sequel to The Talons of Weng-Chiang. Obviously. There are a vast number of references to Greel, the zygma beam, the Time Cabinet and so forth. I haven't noted every one.
A general familiarity with the first half of the Key to Time season wouldn't hurt.
Pg 8 "It was the skull of some sort of animal, perhaps eighteen inches long. He couldn't help thinking that itspointed nose looked like that of a mouse or rat." The giant rats from The Talons of Weng-Chiang.
Pgs 16-17 "He looked at the trio of opalescent crystalline chunks in his hands, weighing them with a puzzled expression." The Key to Time.
Pg 18 "The White Guardian had instructed the Doctor to seek out the six segments of the Key to Time, so that a universal balance might be restored." The Ribos Operation.
Pg 19 "This could be some sort of interference from The Black Guardian: trying to snatch the segments." As he will try in The Armageddon Factor.
Pg 23 "Not a very pleasant time; especially with those stranded Alpha Centauris panicking all over the place" The Curse of Peladon, The Monster of Peladon.
Pg 28 "A few tiny tapestries hung on the walls, and a small platter of food was on a low table before a small obsidian statuette of a grinning dragon with emerald eyes." Smaller version of the one we saw in Talons.
"Stabbed by the look of him. [...] Stomach and maybe up under the ribs." This is similar to Professor Litefoot's diagnosis of the stabbing in Talons.
Pg 34 "Nitinol is currently used by the Draconian Alliance" Frontier in Space et al.
Pg 35 "'And where did they go?' The Doctor strolled around in a small circle, peering alternately at the ground and the sky. 'Hyperspace?' He stopped and shot her a look. 'That wasn't very funny.'" The Stones of Blood.
Pg 38 "I had enough of that sort of thing with Nero." The Romans.
Pg 39 "Vivien Fay used the third segment for interstitial transference into hyperspace" The Stones of Blood.
Pg 58 "Just put Doctor John Smith." Spearhead from Space et al.
Pg 59 "Even the sonic screwdriver won't get us out of this one..." The Invasion of Time.
Pg 65 "She pulled back the sleeve to reveal the sinister black and red tattoo of a scorpion, its stinger uncurled to strike. 'Have you seen anything like this before?' The Doctor looked, his face hardening. 'That explains a lot.' 'You know about it?' 'Yes. It's a Tong sign: the Black Scorpion.'" The Talons of Weng-Chiang.
Pg 78 "A tall man with wide pale eyes and hair that curls like the ram..." Li H'sen Chang's journal, The Talons of Weng-Chiang. Hsien-Ko is Chang's daughter.
Pg 82 "K9, did what just happen to us have any similarity to the effect of Vivian Fay's staff?" The Stones of Blood.
Pg 101 "'Have you ever fired in anger?' 'Just once, a few weeks ago on Zanak.'" The Pirate Planet.
Pg 102 "Woo had never heard of Zanak, though he prided himself on a grasp of general knowledge." The Pirate Planet.
"Behind the altar was a huge basalt dragon with long fangs and five claws on each foot." The Talons of Weng-Chiang.
Pg 103 "She had long since decided to tell Weng-Chiang the story when she met him: of how he, magician Li H'sen Chang and his mechanical killer, Mister Sin, had searched the world for his Time Cabinet, until he found it in London." There follows a lengthy summary of The Talons of Weng-Chiang.
Pg 108 "I'm told he was a caretaker at the Palace Theatrical Museum in London." Presumably what became of the Palace Theatre after The Talons of Weng-Chiang.
Pg 113 "In a way, the thought was saddening, for she knew that - barring accidents - she would outlive Kwok, along with everyone else." The War Games.
Pg 123 "Magnus Greel was no god." The Talons of Weng-Chiang.
Pg 133 "The Doctor perked up. 'A quarry! How very interesting!' He paused. 'It looks a lot like Skaro, actually. Or the land outside the Capitol...'" The Daleks et al, The Invasion of Time.
Pg 154 "The White Guardian warned us to beware." The Ribos Operation.
Pg 157 "Anyway, after Xanxia, then Vivien Fay..." The Pirate Planet, The Stones of Blood.
Pg 159 "Is this the girl Leela with you?" The Face of Evil et al.
"You knew him in London when he was performing in 1889." The Talons of Weng-Chiang.
Pg 167 "The zygma beam; Magnus Greel's zygma beam!" The Talons of Weng-Chiang.
Pg 176 "'What was that dwarf thing?' 'The Peking Homonculus.'" The Talons of Weng-Chiang.
"It massacred the family - supposedly due to some malfunction - and very nearly started World War Six." The Talons of Weng-Chiang.
Pg 180 "It seems Greel was right in a way; the zygma experiment did work, just not in a way even he could envisage." The Talons of Weng-Chiang.
Pg 181 "He's a war criminal with the blood of millions on his hands" The Talons of Weng-Chiang.
Pg 218 "'Those will be KMT troop trains filled with Tong members.' 'Oh, I think we can keep out of their way.' He grinned. 'I always thought everyone wanted to drive one of those someday.'" Black Orchid.
Pg 226 "Self-justidication is a characteristic of trauma-based psychoses.'" Romana's psychological diagnoses were a feature of The Ribos Operation.
Pg 228 "Angle of incidence equals angle of reflection, his targeting systems determined." As K9's will do in Warriors' Gate.
Pg 244 "That lock's a good deal more sophisticated than that old trionic lattice that Weng-Chiang's zygma cabinet used." The Talons of Weng-Chiang.
Pg 245 "I made a few improvements to Professor Marius' design." The Invisible Enemy.
Pg 250 "You'll get the nasty truth of the Blinovitch Limitation Effect." Day of the Daleks et al.
Pg 251 "Greel paid the price for his lack of responsibility. Cellular collapse isn't a very pleasant fate." The Talons of Weng-Chiang.
Pg 263 "Romana had never seen such panic since Gallifrey itself had been invaded not so long ago." The Invasion of Time.
Pg 265 "It wouldn't bother her so much if she hadn't known what Magnus Greel had looked like in the final years, his flesh distorted and scrambled." The Talons of Weng-Chiang.
Pg 282 "You're not thinking of time-ramming it?" The Time Monster.
Pg 291 "I've got a fix on the fourth segment now. It's not on this planet or century at all." The Androids of Tara.
OLD FRIENDS AND OLD ENEMIES
Pg 123 The Tong of the Black Scorpion (from The Talons of Weng-Chiang).
Pg 143 Mr Sin (also from Talons).
NEW FRIENDS AND NEW ENEMIES
Mr Woo, Kwok, Rondo.
Pg 201 T'ai Shan, in the Shangdong province.