The Fifth doctor, Peri and Erimem visit the first great Church council in the year 325 AD. The Christian Church has been divided by the conflicting beliefs of Bishop Alexander and and a man named Arius, and the council is set up by the Emperor in order to establish what be will be considered doctrine. The conflict: Arius believes that God is absolute, indivisible and at the root of creation for the rest of the world, meaning that Christ must be a creation of God, rather than a divine aspect of God's self.
Emperor Constantine hopes that the council will restore order to the Empire by uniting the Church, enabling it to serve as a stabilising influence. Peri and Erimem soon become involved in the politics of the council and find out that some people are willing to kill in order to silence the voices of those who oppose them. Erimem, who has learned that Christianity is a loving religion, is horrified to hear that her new friend Arius won't be allowed to speak during the council and will have to rely on others to speak for him. She would never have allowed such injustice to happy in her own state, had she accepted her position as Pharaoh. Although she's still conflicted about the idea of religion to begin with, she realises that she can use her diplomatic experience to force the council to listen to Arius and stay true to their purported Christian compassion.
Five, meanwhile, gets separated from his companions during the citywide riots, and is thrown into jail. Emperor Constantine is curious about the foreigner who'd want to stop the riots (rather than being on the side of one party), and meets up with the Doctor, asking him to act as a spy or mediator. The Doctor realises this might be a golden opportunity to see the council from the inside, and accepts, not actually planning to meddle in anything.
Erimem and Peri soon find out that the Doctor is siding with their new enemy, Emperor Constantine. Five tries to explain that things aren't quite as black and white as that, and that they really shouldn't start changing history. But during the Church council, Erimem (posing as the Doctor's servant, although the guards still don't like women in the building) stands up and demands Arius be allowed to speak when Bishop Alexander's clerk Athanasius, starts condemning Arius. She's immediately thrown out, of course, and the Doctor is held responsible for his servant's disobedience. Erimem becomes really very angry at the Doctor and asks to be left behind so she can support Arius. The Doctor, meanwhile, loses Emperor Constantine as a friend and instead becomes his unwitting spy, while Peri befriends Empress Fausta and becomes her pawn. In the end, Erimem and Arius stage an uprising, and Constantine finds himself forced to mobilise his soldiers in order to calm the riots. To Erimem's great surprise, the soldiers don't attack — Constantine isn't a monster, just a man in a difficult position. The Doctor explains that Constantine can't force the Bishops to let Arius speak for himself, since exerting that kind of power would make him a tyrant. Things may work that way in Erimem's time, but not for the democratic tail end of the Roman era. Erimem relents, finally accepting that even though Arius has now earned the right to speak, history will unfold as it always did. Arius will be banished, and Constantine, who grows to mistrust Fausta (in part because of team TARDIS), will murder his wife soon after, thinking she conspired against his son, which the Doctor says she probably did. However, Arius will eventually be allowed back into the Roman empire. Erimem apologises for her rashness.
This story is notable for being a somewhat rare purely historical adventure.
- Ambadassador: Erimem really shines.
- Angel Unaware: Arius and Clement think Erimem was one when they see the TARDIS dematerialise.
- Balcony Speech: Constantine gives one to Arius' supporters, telling them he is their Emperor.
- Borrowed Catchphrase: The Doctor uses Two's "When I say run, run!"
- The Caligula: Invoked with Constantine, but there's a lot of emphasis on the fact that he's also an actual person, not just a cruel ruler.
- Continuity Nod: Cardinal Richelieu is mentioned.
- Corrupt Church: That it is religion does not stop it from being a tyranny!
- Disaster Dominoes / Butterfly of Doom: Changing the origins of Christianity in early Rome can potentially mess up current / future Europe.
- Emergency Presidential Address: Constantine gives one to a mob supporting Arius, also making sure his troops stand down.
- The Emperor: Constantine, obviously.
- Evil Overlord: Constantine is perceived as this by some characters. He turns out to be more a man who sometimes has to use harsh methods. Erimem eventually concludes he isn't a tyrant as a tyrant wouldn't use his troops.
- The Fettered: Erimem.
- God Guise: At the end of the adventure, Those Two Guys think Erimem was an angel all along.
- HeelFace Turn: At the end the Doctor says that eventually Constantine exiles Athanasius and lets Arius back into the Empire.
- Historical-Domain Character: Everyone.
- In Vino Veritas: Fausta tries this on Peri. However Peri doesn't let that much slip.
- La Résistance: Erimem is suspected to be part of one.
- Obnoxious In-Laws: It's mentioned Constantine killed his wife's brother, however this was in a battle against him
- O.O.C. Is Serious Business: Five gets angry enough in this episode to shout at his companions.
- Reasonable Authority Figure: Constantine overall comes across as this, stuck in a difficult position and wanting peace. The Doctor even says "He's a good man."
- Torches and Pitchforks
- Well-Intentioned Extremist: Constantine comes across as this with his ruthless methods, killing his brother-in-law because they fought against him, and claims he only uses violence as a last resort. He has to use harsh methods to keep order.
- Written by the Winners: Invoked on Constantine.
- You Cannot Fight Fate: The Doctor says how some parts of the timeline can't be changed.