The Plume Coteries, also known as the Bookkeepers, were a faction of posthuman librarians who operated the Library. (PROSE: White Canvas, A Farewell to R.M.S.)
History
The Plume Coteries were originally a miniscule posthuman peoples who were known to travel on the backs of majestic birds. (PROSE: A Farewell to R.M.S.)
The Coteries colonised the Revelatory Majesty Sphere in the Amazolian system. (PROSE: A Farewell to Arms) The Coteries donated RMS to Roger's family as part of a peace treaty after accidentally desolating the Rogers' homeworld. (PROSE: A Farewell to Arms, A Farewell to R.M.S.)
After discovering the Library, they became predominately known as the "Bookkeepers", (PROSE: A Farewell to R.M.S.) but were still interchangeably called "Plume Coteries". (PROSE: White Canvas, A Farewell to Arms, et al.) Most Bookkeepers became closer in size to classical humans. (PROSE: A Farewell to R.M.S., White Canvas) Some of the Bookkeepers' smaller members acted as dignitaries to the outside universe, using specially-sized diplomatic craft to travel through space. (PROSE: A Farewell to Arms)
When the Great Houses tried to buy RMS from Roger, the Bookkeepers stepped in to help negotiations, postponing the deal for many years due to their lack of field agents. In the interim, they used their books to learn much about the agreements the Houses were making with other powers in preparation for the War in Heaven. When the time came, the Bookkeepers traded RMS in return for the Houses' secrets of time scooping. (PROSE: A Farewell to R.M.S.)
As part of "a long story that could be a book in itself", Coloth was resurrected by the Bookkeepers to act as an agent of theirs. (PROSE: White Canvas) Sometime after this, dignitaries of the Coteries from the "distant reaches of dead space" came to Terra Primagenia to attend the unveiling of Cernunnos. (PROSE: Cobweb and Ivory)
Some Bookkeepers came to the Needle to witness the signing of the Christmas Needle Agreement, where they got into a heated talk with the Firmament. (PROSE: White Canvas)