The world took the form of a medieval castle, and the technological development remained mostly consistent with this impression: the prime weapons were swords, but firearms were occasionally used — most often for ceremonial purposes. The people were ruled over by an emperor, who was proclaimed a god and would rule over his subjects as a (mostly benevolent) despot alongside his wife. All aspects of society were dominated by the ruling monarch, and in turn, his subjects accepted his decrees without complaint, only showing signs of discontent if an emperor ever admitted to not being a god — which would result in his summary execution.
In keeping with his status as a god, the emperor was followed by a royal scribe tasked with recording all events of the sovereign deity's life, no matter how banal, and entering them into a Holy Bible; however, few people would ever read the bibles except for the scribe, for they would only be completed upon the emperor's death — whereupon he would be declared a false god and the bible promptly became invalid.
In reality, the castle was purely a constructed world. Nothing existed outside the castle — indeed, the people had no concept of "outside". Eugene Tacitus, the Emperor's Scribe, was the only real person in the realm and the only inhabitant with any influence other than the Child: all other characters were merely mental constructs created by Tacitus, their lives dictated by his imagination. However, after centuries of imprisonment, Tacitus had forgotten who he really was — apparently out of a conscious effort on his part; he would only become aware of his true identity and power over the fiction at the end of every Greater Cycle. (AUDIO: The Holy Terror)
The Lesser Cycle
Traditions, rituals, and events followed a very specific loop in this world. Upon the death of an emperor, he would be proclaimed a false god (as evidenced by dying) and his surviving wife would likewise be denounced as a false goddess and sentenced to death by torture; throughout the castle, holy depictions of the former emperor would be destroyed en mass, and any citizens who still revered him would be executed for heresy. However, the people's loyalties and worship were easily transferred to the new emperor with only minimal casualties.
Despite the previous emperor being denounced as a false deity, his neurotic son would nonetheless assume his role as imperial ruler. Meanwhile, the new emperor's deformed half-brother, aided by the High Priest, would lead a rebellion against the new regime; however, the coup would fail and both conspirators would be executed. Unchallenged from then on, the new Imperial Couple would slowly become almost identical to their predecessors, particularly in their loveless marriage and growing sadistic tendencies: of the two sons they would raise, one of them would be born disfigured and turn out to be of illegitimate parentage, while the other would turn out soft-hearted and fearful — often suffering abuse from both parents for serving as a reminder of the father's earlier neurosis. Eventually, the emperor's reign would come to an end with his death, whereupon the cycle would repeat once more. (AUDIO: The Holy Terror)
The Greater Cycle
After countless cycles of Royal Succession, a different and larger cycle would unfold as a recurring punishment for Tacitus: his son would be reincarnated as one of the characters within the universe, easily recognised by his face regardless of the character he'd appeared as. Possessed of seemingly limitless power, he would kill everyone in the castle in a homicidal search for his father, ultimately destroying the entire world in the process and rendering it down into formless void. Forced to see the fantasy he had taken refuge in destroyed, Tacitus would remember who he really was and what he had done, and the Scribe would be forced to kill his son once again; Tacitus would then re-build the world and begin the cycle anew, immersing himself in the fiction until he once again forgot who he was.
Into the end of one such cycle stepped the Sixth Doctor and Frobisher. The world was structurally similar to the extra-dimensional space created inside a TARDIS, and it was this that drew the Doctor's TARDIS to it, the TARDIS requiring a similar environment to itself to recuperate after Frobisher interfered with the dimensional stabilisers.
In this particular cycle, Tacitus' son was incarnated as the son of Childeric, the current emperor's half-brother: the centerpiece of a delusional scheme to create a true god, the child had been raised in complete silence so that he would not be "contaminated" by mortal language, Childeric going so far as to cut out the tongues of anyone assigned to care for the child — including his own wife, and later his servant Arnulf. The child willingly played his role as a young god up until he realised that Childeric wasn't his "real" father, whereupon he tore Childeric apart and began his search for Tacitus.
Meanwhile, the new (and final) emperor abdicated his throne to Frobisher, who attempted to break the cycle and give free will back to the people. Unfortunately, the people were massacred before Frobisher could get them to understand the concept. The Doctor also attempted to get Tacitus to break the larger cycle by convincing him not to kill his child, offering to help him escape from the prison once and for all. However, though Tacitus successfully resisted the urge to continue the cycle, he could not forgive himself for what he'd done and had his son kill him instead. With no further reason to exist, the child and the remains of the pocket universe dissolved into nothingness, leaving the Doctor and Frobisher to solemnly depart. (AUDIO: The Holy Terror)