-->'''Donna:''' It's weird, but... being with you, I can't tell what's right and what's wrong anymore.
-->'''Doctor:''' It's better that way. People who know for certain tend to be like Mr Halpen.

The Doctor and Donna land on a gorgeous snowy world -- your favourite alpine vistas, [[UpToEleven cranked up to 11]]--somewhere in the distant future. It is the Oodsphere, home planet of the Ood, the apparently willing slave race we first met in "[[Recap/DoctorWhoNSS2E8TheImpossiblePlanet The Impossible Planet]]"/"[[Recap/DoctorWhoNSS2E9TheSatanPit The Satan Pit]]".

All is not well on the Oodsphere. Ood Operations, the Ood suppliers to the galaxy, are sitting on a disturbing fact: Ood everywhere have been going berserk and killing their masters. The only symptom is that the Ood's eyes will turn red just before it snaps.

The Doctor and Donna sneak off to interview some Ood, but the only hint the Ood themselves can give is that "the circle must be broken"[[note]]By and by, Lord; by and by...[[/note]]. The Doctor and Donna discover, to their horror and disgust, that the process that wild Ood undergo to turn them into slave Oods is... lobotomy. The communication orb isn't just an addition to their bodies: it's a ''replacement'' for their second, external brain. The Doctor gently connects to Donna telepathically and makes her hear the collective mind-song of those Ood that are still intact.

But even the unaltered Ood are being restrained somehow -- something is holding back their song. That's when they come across the ''third'' brain of the collective Ood consciousness, a giant mass imprisoned in a ring of machinery and electricity -- the circle which must be broken.

They save the Ood [[Recap/DoctorWhoS24E1TimeAndTheRani using the tried and trusted method of blowing things up]], hear their Song Of Freedom, and receive in return a cryptic message about the Doctor's song ending soon.

* BatmanGambit: Ood Sigma's "hair tonic".
* BodyHorror: Halpen's "hair tonic" turning him into an Ood. His hair and scalp peel away revealing an Ood head, and tentacles spill out of his mouth, followed by a brain.
* CallBack: The destruction of the circle around the third brain is very similar to [[Recap/DoctorWhoS24E1TimeAndTheRani a scene from the classic series]].
* ChekhovsGun: The drinks Mr Halpen keeps knocking back are blatantly going to bite him ''somehow''. Boy, do they ever.
* CorruptCorporateExecutive
* ContinuityNod: Oodsphere being in the same system as Sensphere, home-world of [[Recap/DoctorWhoS1E7TheSensorites the Sensorites]].
** The Doctor is all gleeful to walk out and find a snowstorm of ''actual snow''. (The last few times it's been, respectively, [[Recap/DoctorWho2005CSTheChristmasInvasion the ashes of a Sycorax spaceship]], [[Recap/DoctorWho2006CSTheRunawayBride bits of Racnoss web and artificial snow expelled by the TARDIS]], and [[Recap/DoctorWho2007CSVoyageOfTheDamned ballast dropped by a damaged interstellar cruise liner]])
* DistressedDude: The Doctor tied to a pole.
* FantasticRacism: Emphasised by the fact that the whip-happy slave overseer is a black guy, and the PR representative who is tasked with justifying slavery to the audience is Indian.
* {{Foreshadowing}}: The Ood refer to the Doctor and Donna collectively as the Doctor-Donna. It takes the rest of the series for the Doctor to figure it out, but when he does, he thinks it's all quite clever.
** [[MotorMouth Partly because of the way he introduced themselves to the Ood in the first place]]. Truly an example of FridgeBrilliance.
* HappinessInSlavery: Subverted after being set up way back in "The Impossible Planet".
* HeyItsThatGuy: Mr Halpen is [[Series/{{Blackadder}} Percy/Captain Darling!]]
* HoistByHisOwnPetard: The overseer who tries to gas the Ood ends up being the only victim of the gas.
* IgnoredEpiphany: The PR representative.
* ImproperlyPlacedFirearms: Guards with M4s and a guy with a PPK; in the 42nd Century. Though [[KineticWeaponsAreJustBetter it is currently believed that small arms have hit a peak where making them any more powerful would make them uncontrollable]].
* KarmicDeath: The PR rep is zapped after rejecting the Doctor's offer to stop the injustice against the Ood, and the overseer is gassed to death with the same gas he tried to use on the ood.
* KarmicTransformation: Halpen.
* LongSpeechTeaTime: Donna's first impression of the Oodsphere is that it's freezing. The Doctor encourages her be more awestruck by the setting, consider how last week she was in Chiswick just getting up, working, coming home, watching telly and going to bed and now she's travelling across space and time to land on alien worlds... then finds she's gone back into the TARDIS to get a coat.
* MaamShock: Inverted -- Donna reacts to being called Miss. "Why do you say Miss; do I look single?"
* NeverTrustAHairTonic: Mr Halpen's hair tonic... isn't.
* PetTheDog: Despite his attitude towards the Ood at large and his general asshattery, Halpen seems to be genuinely quite fond of Ood Sigma for most of the episode.
* RailingKill: When Dr Ryder reveals he's a Friend of the Ood, Halpen pushes him over the rail and ''into'' the Ood brain.
* RedEyesTakeWarning
* RetroRocket: Of a similar design to the one from the last Ood episode. Donna approves ("You've got a box, he's got a Ferrari!").
* ReverseMole: Dr Ryder.
* SheIsNotMyGirlfriend: "Pleased to meet you, Doctor Noble, Mrs Noble."
* ShoutOut: The "comedy classic" Ood is programmed to say "[[WesternAnimation/TheSimpsons D'oh!]]" when it drops something.
* WeWillUseManualLaborInTheFuture
* TheXOfY
* ZergRush: A perpetual favourite of berserk Ood.
[--There's a better / home a-waitin' / In the sky, Lord, in the sky--]