As for the rest of TCB from that point (the return to Estengard) onwards, here's my attempt at a summary. (I must confess that I had to look up a few details!)
×Drokkendut (spelled with only one T here, two in GatEB) listens to Beethro's warning against the Empire, but says that Beethro's words don't have much weight with him. Frustrated, Beethro returns to the City. He overhears the gossipers refer to him as "
1st Slayer"
, and realises that, having killed the other Slayers, he can now go through the Gate of Firstity.
This leads to the Asking Chamber, where a citizen conveys questions to Lowest Point through a speaking tube. Beethro asks whether the DAA are really working in the surfacers' interests, but gets an inconclusive response. Outside, the Pit Thing says that the first person Beethro met in the City can help him, and Beethro realises this means the Infohut guy. He asks how he can get to Lowest Point, and the Infohut guy lends him a rope to descend the three-mile abyss.
At the foot of the abyss, Beethro encounters the Stalwart Army from Tueno (and I've heard that Tendry appears here, though I don't remember meeting him). They have come to battle the Empire, and are confident of success since the Slayers are dead. Unfortunately, the batch of Aumtlich are ready, and the battle turns into a massacre.
But the Empire forgot something that Beethro could have told them:
never trust a goblin. The Goblin King has, in secret, been preparing to turn on his former allies, building a briar trip. A goblin named Gristy opens the briar trap, completely turning the tables on the Aumtlich. Beethro realises that his remaining allies cannot defeat the Empire by force, and so he continues his quest for Lowest Point to gain knowledge.
Beethro fights his way through the Aumtlich fortress (much easier now that the Aumtlich army is depleted, but still the hardest level of the game!) and reaches Upper Lowest. The Patrons, agreeing with the Archivists that Beethro must not reach Lowest Point, send Halph to stop him. Halph and his team of builders obstruct Beethro in every way they can, but he eventually gets through.
At Lowest Point, Beethro finds only the corpse of 1st Watcher, and realises that the Asking Chamber was a sham and no-one was running things. He steps on a trapdoor, and it falls into the Second Sky. Oh, and I'm not quite sure how Beethro ever got back up, considering Halph's builders had blocked off the stairs up in Lowest Proper : The Entrance
