The Investigators of Down Cthulhu
Revelations of Glaki
Taken from Boston HQ of The Silver Twilight/
Written in England, 19th century.
Several major libraries have copies, in 9 volumes. There are rumors of copies of a few more volumes. Glache is supposedly and alien, possibly a Venusian, who was knowledgable of much about the Mythos.
This volume in my very hand is marked as volume 11!