One (The Book of the War)

Several parts of The Book of the War and the Book of Lies attached significance to the moniker or descriptor "One" as something relating to the nature of the enemy during the War in Heaven.

Umbaste's vision
After President Umbaste opened his biodata to the caldera, he was launched into a fugue state as his mind wandered the meta-structure of history. When he eventually returned, all he could say was a single word, over and over; when stripped of its time-active connotations, the word could be translated to the English language as "One". After several days of this, he killed himself. (PROSE: The Book of the War) However, the secret minutes of House Dvora suggested there was more to his death. (AUDIO: A Labyrinth of Histories)

Carmen Yeh's account
Carmen Yeh's Fantastical Travels in an Infinite Universe contained an account of a momentous interview between Compassion and the War King during which the two discussed their respective views on the identity of the enemy, and brokered an uneasy alliance. When one of the War King's advisors asked what "assurance" she could give of the safety of the breeding pair of pilots she demanded as payment for joining the War, she willfully misinterpreted it as a request for an assurance of the reality of the threat they all faced. Answering that imaginary question, she tapped the golden circlet the advisor was wearing, (PROSE: The Book of the War) used to link one's mind into the Matrix, (TV: The Invasion of Time) and said: "what do you have for assurance? I can answer that one quite easily. As a matter of fact, I think you can answer it yourself quite easily. You know where to look. As to what you'll find there… one thing. Just one". (PROSE: The Book of the War)

The Book of Lies' account
An aphorism of the Enemy contained in the Book of Lies read, "One does not love or hate: One is not a person nor a gestalt." (PROSE: Pre-narrative Briefings)

In the Rivera Manuscript
The Rivera Manuscript described a Great House renegade's imprisonment by mysterious forces. Commentary on the Manuscript in The Book of the War suggested that the renegade "had fallen into the hands of the enemy, already studying the Homeworld’s weaknesses long before the War’s outbreak". These enemy representatives were never directly described, although the manuscript referred to a humanoid form, a non-carbon presence, and something the renegade called "the first, the many, and the indivisible" (which "may have been a bad translation").

In parts of the renegade's subsequent praxis-induced vision of the Event, he was accompanied by someone called "One". Though there seemed to be difficulty translating the relevant section of the Manuscript into English, some sections were legible: an interpolation reading "why does it hate us?" and, later, an extended conversation. (PROSE: The Book of the War) "Is that what you're planning / It might be / It still could be / Remember / Inside the skin of the sun / It's an option / It wouldn't work / What if someone tried it / What if you were called to account / It's an option / Always an option / You keep the sun / In a bottle / You want to know what happens if you lose control / Don't you?"

- The Rivera Manuscript

Shortly before her death, Thessalia sent an unprecedented order directly to the ruling Houses, insisting they perform a thorough spectroscopic analysis on the Homeworld's sun.

The Book's commentary also noted that the renegade’s physical captors were probably "mere proxies", rather than the Enemy itself being present. It made note of the fact that One was "a title known to be taken by the head of the Celestis's Investigators", but proposed that this was likely a coincidence because "the Celestis [weren't] mentioned anywhere else in the text". (PROSE: The Book of the War) Notably, another account showed that Investigator One went rogue during the War following the fall of Mictlan, after a "brush with death at the hands of the Time Lords which had left him still humanoid, but somewhat less than real; "his features were blurred, like an unfocused photograph of a man". (PROSE: The Taking of Planet 5)