Citadel of the Autarch, Chapters 27 to 30
Vodalus speak to Severian and is torn between his desire to reward Severian's loyalty and is promise to give Severian up to Agia. Vodalus wants the Autarch delivered to him, and reveals he doesn't know that the Autarch was his servant. Severian is forced to march with the army, and later meets the Autarch again, who relinquishes his life that he may be absorbed by Severian. Severian passes out from the strain of the absorption, and awakes in the clutches of Agia once again, who plans to kill him. However, the Green Man (a time traveller encoutered in Book 2) is there to rescue him. A flying ship arrives and Master Malrubius and his old dog Triskele step out to greet Severian.
[Edited by @Apocryphal]

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Comments
Other thoughts... we had a quick flash forward to a later ceremony of mysterious import.
I'd forgotten about the green man (foolishly, as we were promised he would return). It wasn't altogether clear to me what Agia's game is... did she rescue Severian from the Ascians out of altruism, or simply so that she could wreak her own revenge?
And it's totally confirmed to us that the Autarch has to absorb all previous versions of him/herself. I thought that the shock of transition was very convincing. And how interesting that he now has a more realistic view of his other selves, eg Thecla is recognised as in many respects a "cruel and foolish woman" rather an idealised partner.
I'd like to note briefly that this section should really be chapters 27-30. I've edited the OP on Paul's behalf (since he's quite busy) and re-written the summary of events to reflect these chapters.
Here's the remaining schedule:
Week 39 (11th December - this past week)
Chapter 27: Before Vodalus
Chapter 28: On the March
Chapter 29: Autarch of the Commonwealth
Chapter 30: The Corridors of Time
Week 40 (18th December)
Chapter 31: The Sand Garden
Chapter 32: The Samru
Chapter 33: The Citadel of the Autarch
Chapter 34: The Key to the Universe
Week 41 (28th December; slightly later because I doubt we want to discuss on Christmas Day)
Chapter 35: Father Inire's Letter
Chapter 36: Of Bad Gold and Burning
Chapter 37: Across the River Again
Chapter 38: Resurrection
I'm fairly sure Revenge is one of Agia's motives, but I also wonder if there are more - like direction from Erebus?
Interesting the Vodalus seems to have no idea his erstwhile servant was the Autarch. He knows Severian and the Autarch were on the craft together when it crashed, but thinks that means Severian is either the Autarch, or that he's lying that the Autarch was with him.
There's an interesting exchange with Malrubius in chapter 30:
He then seems to refer to himself as a Deus ex Machina (which I know @clash_bowley will just love!)
No sense in not spelling out to the audience what is happening in the show!
Thanks Chris for looking after this. The next one will be up in a matter of minutes.
LEXICON
Cerbotana: A mispelling of the Italian word for blow-gun: cerbottana.
Uturuncu: Quechua word for 'jaguar'. I don't see any independent reference to this being a shaman who can turn into a tiger. The word does not appear in the Lexicon Urthus. One author of a study of The New Sun thinks that the shaman in this scene is actually Father Inire.
Curtelaxe: old form of 'curtle-axe', which is a type of cutlass or cutting sword.
Ransieur: A pole weapon with a 3-pronged head.
Uintather:

Platybelodon:

Pteriopes: Winged creatures with stag heads - i.e. perytons.