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->''"There is a school of thought somewhere that equates the Borg from Star Trek with the Cybermen from Doctor Who... However, I believe the Borg owe just as much to the Wirrn."''
-->-- '''Gary Russell'''

All the Doctor and Sam wanted to do was go to a wedding. Two of the Doctor's companions, Stacy the Human and Ssard the Ice Warrior, are getting married. They've picked a beautiful place for it too: an artificially constructed world called Micawber's World, built out of an asteroid.

Unfortunately, when the Doctor is involved, nothing ever happens as planned. To start with, the [[Recap/DoctorWhoS12E2TheArkInSpace Wirrrn]] (yeah, the [[SpecialEffectFailure bubble wrap ones]]) are in the midst of invading Micawber's World. For another thing, the artificial world is playing host to the Olympic Games™. And for a third, there's this strange cult called the Church of the Way Forward protesting the [[InterspeciesRomance interspecies wedding]].

Shortly after Stacy and Ssard are happily sent off on their honeymoon, the Doctor begins investigating a number of these strange events. The investigation is made a bit more complex by the fact that even the ordinary Federation humans and aliens are double-dealing, lying, and generally causing trouble unrelated to the impending Wirrrn invasion. However, through a combination of asking the right questions, somehow managing to get on everyone's good side (practically a first for the Doctor), and knowing more than everyone else, the Doctor figures out what's going on.

Meanwhile, Sam investigates the Church of the Way Forward, gets into long religious debates, and generally doubts her own beliefs. She, as usual, ends up running into trouble, but this doesn't help the Doctor's investigation much, since he's already figured out what's going on by the time they're reunited.

By then, however, it already seems like it's too late.
----
!! Tropes present in ''Placebo Effect'' include:

* TheAssimilator: The Wirrrn.
* AuthorFilibuster: The debate between Sam and Reverend Lukas seems awfully like one
* ContinuityNod: Stacy and Ssard are companions of the Doctor from a relatively obscure line of comic strips in the ''Magazine/RadioTimes''. It's revealed in the story that the Doctor had those adventures while Sam was dropped off somewhere, but returned for her before she knew he'd been gone.
* ContinuityPorn: Pretty much everyone in this book comes from some previous episode/book/comic.
** The Wirrrn ([[Recap/DoctorWhoS12E2TheArkInSpace Ark in Space]], but spelled with an extra "r" like in the novelisation of said story)
** The Foamasi ([[Recap/DoctorWhoS18E1TheLeisureHive The Leisure Hive]])
** Stacy and Ssard (Radio Times Eighth Doctor Comic Strip)
** A Meep (The Star Beast - Fourth Doctor Comic)
** Kleptons (Klepton Parasites - First Doctor Comic)
** SSS ([[Recap/DoctorWhoS3E4TheDaleksMasterPlan The Daleks' Master Plan]])
** The Federation ([[Recap/DoctorWhoS9E2TheCurseOfPeladon Curse of Peladon]], [[Recap/DoctorWhoS11E4TheMonsterOfPeladon Monster of Peladon]])
** Also, The Eighth Doctor, it seems, is once again [[Recap/DoctorWhoTVMTheTVMovie half-human]]. He can also tell details of random people's futures.
* FantasticRacism: Sam is rather offended when Kyle says that all Meeps look the same.
* FullyAbsorbedFinale: The Stacy and Ssard plotline wraps up the story of Russell's short-lived Magazine/RadioTimes Eighth Doctor comic strip.
* TheFundamentalist: Reverend Lukas and his Church of the Way Forward
* InterspeciesRomance: Stacy and Ssard. The Church of the Way Forward takes issue with this.
* ShoutOut: Lots. All of the Foamasi use voice synthesizers based on 20th century Earth actors.
** The Foamasi who works in Room 101 uses a voice synthesizer based on [[Creator/RichardBurton Richard Burton]], who played O'Brien in [[Literature/NineteenEightyFour 1984]].
** Another is John Gielgud, from [[{{Film/Arthur 1981}} Arthur 2: On the Rocks]].