Roots: Medieval freakshows and menageries, post-apocalypse stories.
Goofs: For a genetically engineered super-warrior, the Mecrim encountered by Zoe, Disaeda, and the twins doesn't fight very well. Perhaps all that time in cryogenic suspension dulled its reflexes.
On page 94, the Doctor and Himesor enter the sewers with a lantern - "its naked flame covered to minimize the chance of explosion." But gas explosions don't work that way. If the flame were exposed at all, then it would cause an explosion, and if it wasn't exposed at all, it would go out. In short, you don't take a lantern into a sewer!
Technobabble: Micro-switched magnetic seal.
Dialogue Disasters: A city guard: 'My ma's a great lover of roast tongue, and she ain't too partial where it comes from.'
Reisaz on the Mecrim: 'I'd forgotten how ugly it was.'
Dialogue Triumphs: The Doctor: 'Your superiors will be most annoyed if I am not handed over to them without delay.'
The Doctor: 'Well, that tends to be the normal pattern of things.'
Kaquaan: 'We shall be as silent as a cloudless sky.'
The Doctor: 'Unlike civilian equipment, military hardware is built to last.
Zoe: 'Any ideas?'
The Doctor: 'Yes. We need a stronger door.'
Continuity: Heddeigé is known for his anthropological approach to the discrete development of non-contiguous equivalent cultures. This means that 2 identical societies would evolve along completely different lines. It was a radical expansion on Grotski's second law of cultural retrenchment. Zoe knows this, so it was probably established during her era, or she learnt it from the TARDIS library.
The city is run by the Knights of Kubaris, who despise history and only allow licensed science - the furnace, an electricity generator. The knights' relics include powerpacks and the white 'ceremonial armour of Kubaris', actually protecting against swords, germ warfare, dumdum bullets and noxious fumes [including nerve gas]. The suits have inter-suit communication. The Kubaris have access to clockwork technology allowing someone to create a working dummy of themselves (masked).
The Doctor knows how to make someone think he's paid, when he hasn't. He is fond of Cluedo. He has always thought entomology faintly disquieting. His pockets contain sweets, prize marbles, a compass, a teabag, some pencils, a paper clip, an 8 track cassette and some kind of electrical testing device.
Zoe has recently persuaded the Doctor to install an orthopaedic bed in her room. She has degrees (plural). She has seen dramatic reconstructions and archive film of circuses but never actually been to one.
Jamie was used to tracking redcoats through the heather.
The underground races are the ape-like Rocarbies, the shrew-like Dugraq, the moth-like Taculbain and the Mecrim. The Taculbain are dependant on their queen and they have a period of hibernation when some guard the rest. The Rocarbies treat the Taculbain like gods. The Taculbain grow a variety of plants. Their leaves can trigger Taculbain physical transformations, such as into warriors, changing gender, and changing a few rare individual Taculbain into a queen. At least one of these is capable of drugging humans.
The Mecrim track their victims by heat, have some hearing and can't quite reach people clinging on to their backs. They are 1.6 metres to the shoulder, weigh up to 150kg, reach sexual maturity in 2-5 years, mate late spring - summer, have a 6 month gestation period, have 1-2 young at a time, no external gender differences, lives in large social groups. Its lifespan is estimated at over 20 years. They eat large mammals, carrion, supplemented by berries and bark. They have 4 arms, an internal skeleton, vestigial exoskeleton and secondary jointing. The top layer of muscle is a skin substitute. They have 4 toes at right angles. IT has 4 digit hands on two arms and hooked claws on the other two, which are able to push through materials almost by a phasing effect. There were originally 27 of them. One of their gut microbes is fatal to humans.
Links: Jamie refers to his time on the LIZ (The Space Pirates). The Doctor tries to think of Det Sen (The Abominable Snowmen) and phrases from his recent past come to mind. The Mecrim DNA was owned and licensed by the Butler Institute (Cat's Cradle: Warhead). [Although the Butler Institute had merged with Eurogen a few centuries before (Deceit), they may have later created a subsidiary using the old name.] Zoe recalls the Doctor telling her about the events of The Evil of the Daleks (between The Wheel in Space and The Dominators).
Location: The nameless city of the Knights of Kubaris. It is several centuries after the suits were made, which must have been about 2417.
Future History: During the war with the Draconians c. 2417, project Mecrim genetically engineered killer creatures designed to inflict major casualties on Draconian troops and civilians. The project had the ancestors of the Dugraq to experiment on and the ancestors of the Rocarbies to provide cheap labour for IMC (The Space Pirates, Colony in Space, and Lucifer Rising). The Taculbain were kept for research into their collective mentality. The research centre was closed when its people were killed by Mecrim gut microbe 23d.
Unrecorded Adventures: The Doctor says that he once had a friend who he had everything in common with, but this friend enjoyed being scared of the dark a little too much, and it swallowed him. This could be a reference to Koschei/The Master (The Dark Path). He also has Robbie Burns' shopping list (including freedom and whiskey).
The Bottom Line: A strong plot, strong characters (even if the TARDIS crew aren't very well characterised for the first half of the book). The story didn't even suffer from confusion despite all the different factions involved. Thoroughly enjoyable.