Sting of the Zygons
Roots: Invasion of the Body Snatchers. There are references to Rupert the Bear, Opel, Chitty-Chitty-Bang-Bang, Gosford Park, Pathé, CNN, Scooby-Doo, Sugababes, Rover, and the Milky Bar Kid. The Doctor quotes Oscar Wilde ("The unspeakable in pursuit of the uneatable") and Wordsworth.
Goofs: The Doctor appears to have forgotten the events of The Bodysnatcher.
Dialogue Disasters: "An erudite and gentle maiden accompanying such a cocksure young rip!"
Continuity: Zygons can sting to stun, maim or kill. Their barbed stings are in the palms of their hands (see The Bodysnatcher). No human can survive the full power of a Zygon sting. Zygons smell of earth and iron. The Zygons can hunt humans by scent, having a very sensitive sense of smell. As well as humans, Zygons can take body prints from animals, and use dogs and cows here. Zygon hatchlings have pale, maggoty skin: until they are fully mature, they are mute and have only limited intelligence. The amber is a powder that the Zygons use to place themselves into suspended animation, which they refer to as "the long sleep". Diastellic transmissions leave a trace resonance in the airwaves for up to two weeks. Remars is a Zygon measurement of frequency. Brelarn's plan is to replace the heads of Europe with Zygons, and gradually take over, preparing the world for Zygon conquest. After Brelarn's death, the Doctor tells Taro to transport her ship to the Arctic or somewhere else uninhabited by humanity and return to her people to the amber.
The Zygons here have two Skarasens: the stellar catastrophe that damaged the Zygon ship also affected the brain-computer interfaces of the Skarasens, so that when they were fully reared their brain tissue became inflamed and they became deranged, causing the Zygons to lose control of them. Attempts at diastellic therapy in the adult only aggravated the inflammation, the feedback swamping the control cortex and killing one of the Skarasens by causing its brain to explode. The juvenile survived but remained uncontrollable. After Brelarn's death, the juvenile Skarsen returns to the lakes with the corpse of the adult to live out its life in peace.
The Doctor is trying to take Martha to visit Minkowski's address to the Assembly of German Naturalists and Physicians in Berlin in 1908 at the start of the story. The Doctor really likes picnics and picnic baskets. The sonic screwdriver starts a car here: the Doctor (possibly facetiously) claims that his sonic screwdriver dealer was giving away a Vintage Earth Engines software bundle free with every Sanctuary Base upgrade. He rides a horse. He obtains money for the period from the TARDIS. He has a sixpence in his pocket.
Martha dresses in a gauzy green silk dress with a gold leaf pattern and a close-fitting bead jacket here. She later dons Clara's long fawn overcoat, flowing khaki wool skirt trimmed with black satin, and a woollen shirt-blouse patterned with dark check. She takes Clara's cardigan with her in the TARDIS so that she won't forget her death. She eats bacon here. Martha loved ponies as a child, but doesn't have much experience of riding one: however, she rides one here. She doesn't know how to play Bridge, Bezique, or Bid Whist.
Links: Terror of the Zygons. Martha claims she's had enough of New York (Daleks in Manhattan/Evolution of the Daleks). She again claims to be from Freedonia (The Shakespeare Code). The Doctor mentions his expertise with augmented delta waves (Kinda). The Doctor notes that he used to be an autocar enthusiast, a nod to the Third Doctor.
Location: Templewell, Kelmore, Wolvenlath, and Goldspur, the Lake District, over several days from 16th September 1909.
Unrecorded Adventures: The Doctor may know Minkowski. He also claims to be friends with Asquith and Lloyd George. He also claims that he cleaned out the stables on the planet Augea with Hercules and also had to much out Cerberus.
The Bottom Line: Hugely entertaining fusion of old and new, with Cole on fine form. The Zygons are perfectly captured (and they get some enjoyable development, such as their ability to disguise themselves as cows!), serving once more as a reminder of why they remain so popular despite only once appearing on screen. An ample cast of memorable supporting characters helps to drive the plot along merrily.