Within the PPC universe, World One is largely considered to be synonymous with the Real World. However, it isn't. It is a literary representation of the Real World, just like any other continuum presumed to be set in "reality." The Real World and World One are virtually indistinguishable except that PPC Headquarters exists in World One and can be accessed by plotholes, portals, and Doors. If observed closely enough, World One's Phobos may be seen trying to visit his wife in the PPC Archives, and World One's Huinesoron may not be found on World One's Earth (he may have fallen into PPC HQ through a plothole in his backstory, but this story has not yet been told). Whenever a PPC character interacts with places or people from the "Real World," they are really interacting with the analogous places or people in World One. This includes their own authors, literary representations of the real people behind the keyboards, virtually identical except for their ability to interact diegetically with the fictional PPC.
Perhaps the clearest illustration of the difference between World One and the Real World is New Caledonia. In World One, the PPC has established a small city in the mountains of New Caledonia and can travel freely between it and Headquarters. Measures are taken to prevent the PPC's existence from being too obvious, because all the fictional technology and such would upset the course of history, but a normal person from World One would most likely find the place if they were really determined to go there. However, if you went to the same location in the Real World, all you would find is a mountain with some old mining sites and hiking trails on it.
Most agents are not aware that World One is not the Real World and might go insane if they found out, so it's best not to tell them. Just imagine how you would feel if you found out that you had an author, and then you found out that that author was just a fictional representation of the actual author writing you both. Does your brain hurt yet?
What's Reality, Anyway?
Many agents are from World One and consider it to be the real world. However, opinions on what the "real" world is may differ depending on who you ask. On entering HQ, agents recruited from Middle-earth or Narnia may feel as if they left their real world just like any agent from a world that looks more familiar to us. To avoid misunderstandings and broken skulls, the Flowers encourage referring to universes by the DES's numbering system rather than by ambiguous and emotionally charged adjectives like "home" or "real."
Alas, we don't know this numbering system in detail. We only know that World One is given the primary designation by the Flowers of the Department of External Security tasked with cataloguing all the Word Worlds during their early exploration of the multiverse. To the Flowers, World One appears to be special. It is distinguished from alternate universes very much like it by the fact that all the creators of all the Word Worlds exist in World One, author, Suethor, and Boarder alike. Further, as opposed to the Word Worlds, it is the only universe in the Prime Multiverse where the Flowers cannot read the Words. Thus, the Flowers assume that World One is an "atomic world," not made of letters.
The Flowers are obviously wrong. We can read, and even write, the Words of World One. The Flowers' inability may be due to this being their home universe. (Whether agents can read the Words in canon worlds or only in fanfiction has not yet been determined, mainly because agents legally vacationing in a canon world involves so much paperwork that there are essentially no official records of such visits.)
Just as the Flowers cannot read the Words of World One, we cannot read the Words of the Real World. Whether this is sufficient evidence that we live in an "atomic world," or whether someone may be writing Real Life, is anybody's guess.
PPC Interactions with World One
The PPC limits its interactions with World One on the whole, since messing up the timeline of what they believe to be reality itself would be very bad. However, World One was the primary if not sole source of recruitment for the PPC for about twenty years: since Anya and Elisabeth were accidentally transported into Headquarters in the nineteen-eighties until Jay and Acacia normalized the practice of recruiting from fanfiction in the early twenty-aughts. People sometimes fall through plotholes into Headquarters; the Flowers have sometimes run job ads and recruitment pamphlets in World One, trusting that most people won't take them seriously; sometimes people discover the PPC by coming across mission reports published on the Internet; and sometimes people discover one of the multiple Doors into Headquarters from World One.
One such Door is 1-Nou-1 in New Caledonia, where the PPC has an actual city. It is not a large city, and it keeps a fairly low profile to prevent magic and advanced technology from disrupting World One's history, but it can be found by anyone who is determined to go there.
World One is (usually) the world by which the HQ Standard Timeline is determined.
Missions in this Continuum
Fics that take place in World One tend to be Real Person Fics or fics that involve trans-dimensional snatching. The former sort are no longer handled by the PPC but are listed here; the latter sort can be found listed under the characters' home continua.
- Agent Trojanhorse (DBS) - missions are NSFW