Roots: The Lord of the Rings (a device of enormous power must be destroyed by immersing it in the place of its creation) Red Riding Hood ("What big teeth he has"). The Guardians and Freedom play bridge (shudder). Honore de Balzac's Mercadet ("This is some fresh trick!"); a Teuthoidian paraphrases a broadcast supermarket announcement ("clean-up on deck three!")
Dialogue Triumphs: "My name is unimportant" "-Shy? Or could your parents not come to an agreement?"
Double Entendres: "Finding my serene spot is a bit tricky"
Continuity: The Chaos Pool is a body of water at the foot of a waterfall deep within the planet Chaos, hidden away by a temporal barrier six minutes from the end of known time. For the first time the proposition to destroy the deteriorating Key to Time as a way of saving the Universe is established, and in effect this is what it does. The destruction of the Key disperses the Grace throughout all time, after the reinvigourated Guardians are returned to the "howling void" to resume their eternal battles.
The Teuthoidians are among the Universe's first space faring races, resembling giant humanoid slugs. The environment in their warp spaceships is humid, with the floors covered in a colloidal mucus to allow the crew to move around at will. They are cannibalistic.
The Atrion Alliance exists at a time closer to the end of the Universe and therefore shouldn't naturally be at war with the Teuthoidians. Their lady President Astra reveals is over 200 years old, having survived for so long unconsciously by drawing off the energy from those around her, as a side effect of her release from the Key to Time. As such, the 'Atrion' curse of premature ageing means that the average life expectancy is twenty-nine years.
Zara and Pargrave met on Atrios after she discovered he was the sixth son of the sixth generation of his family. Knowing he would eventually be drawn to the Chaos Pool she grew close to him to exploit his ability to locate the Pool, but after looking after him for months after his partner and children died, never expected to fall in love with him. Amy becomes afraid of dying, convincing the Doctor how much she's changed in the few weeks she's been "alive".
Temporal fluctuation causes the Eschaton to "wobble".
Romana doesn't like castles and recognises the effigies of the Valdigians by their distinctive locust-like wing patterns. She remarks that the Doctor "can't see the storm that's coming" (perhaps a reference to The Apocalypse Element?) Romana explains that after Astra was returned to Atrios, the segment was hidden within her. She didn't realise at first, but this is why her first incarnation decided to change her appearance. Upon her return from E-Space she was unable to regenerate (see Box-Out) and became President of the High Council; she returns to Gallifrey at the end of this story to encourage them to accept non-Gallifreyans into the Academies. It may be inferred that her restoration after the removal of her segment of the Key to Time returns her ability to regenerate.
The Doctor makes telepathic connections with Gallifrey as well as Romana in the form of an SOS.
Location: The planet Chaos at the end of recorded time.
Untelevised Adventures: Romana remarks that Mars "...isn't as I remembered it".
Links: The Armageddon Factor, Destiny of the Daleks, the E-Space Trilogy. Romana quotes the Sixth Doctor in The Caves of Androzani ("You were expecting someone else?"). Zara refers to the planet Eratoom and the first segment (The Prisoner's Dilemma)
The Bottom Line: Nothing good ever came from the sound of giant slugs. There's a lot going on here, including the return of Romana, the resolution to the Key2Time, the fate of Amy and lara and the Guardians, not to mention a Great Richard Harris impersonation. The reveal that Romana is now the sixth segment is a great twist after the twist of her initially playing Astra, but despite the Doctor's self sacrifice, you can't escape the disappointing conclusion that Chaos Pool ends with an enormous short-circuit.
THE REGENERATION OF ROMANA
Big Finish provides two explanations with regard to the regeneration of the Lady Romana at the beginning of Destiny of the Daleks. In the Gallifrey series (Gallifrey: Lies) the genetic presence within Romana of the malevolent and ancient being Pandora is discovered to have existed in a dormant state for most of her life. During her first incarnation Romana's torture by an agent of the Black Guardian released the hidden memories of her early encounter with Pandora and, by implication, her influence. In order to overcome both, Romana forces a regeneration to banish both the presence and her memory; though her memories are indeed reburied, the further events of Gallifrey reveal this to have been in vain. Alternatively, The Chaos Pool offers the explanation that Romana regenerated as a consequence of her absorbing the sixth segment to the Key to Time, resulting in her taking the appearance of the segment's previous form (Princess Astra) and losing the ability to regenerate further. The two explanations may not be mutually exclusive: certainly in The Chaos Pool Romana ought to have no memories of Pandora, these not having yet been unlocked again since her change of body, so her explanation here is reliable in as much as this is all she recalls of the facts.