Eugene's World

Eugene's World was a pocket universe created as a prison for Eugene Tacitus as punishment for the murder of his son. It is not known who created the world or how, though it is implied that (given Tacitus' secret position of control over the pocket universe) the punishment is at least partially self-inflicted.

Society
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 a King, 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 King; in turn, his subjects accepted his decrees without complaint, only showing signs of discontent if a King admitted to not being a god - which would result in the King's summary execution.

In keeping with his status as a God, the King would be followed by a royal scribe tasked with recording all events of the King'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 with the King's death - whereupon the dead King 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 King'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 and only became aware of the power he had 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 the previous King, his elder son would be proclaimed the new King. Having proved the old King to be a false god (as evidenced by dying), any who still revered the old King were viewed as heretics. However, the people's loyalties and worship were easily switched to the new King.

The old Queen would be imprisoned, tortured, and killed. The new King's younger brother, aided by the High Priest, would lead a rebellion against the new King's rule, which would end in failure and the execution of both conspirators. United in a loveless marriage, the new King and Queen would raise two sons, one of whom would invariably be illegitimate, and the cycle would repeat upon the new King's eventual death.(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 recognized 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 castle 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.

In this particular cycle, Tacitus' son was incarnated as the son of Childeric, the current king's illegitimate 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 realized that Childeric wasn't his "real" father, whereupon he tore Childeric apart and began his search for Tacitus.

The new (and last) King 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, while Tacitus 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. (AUDIO: The Holy Terror)