If a little knowledge is a dangerous thing, then a lot of knowledge is a critical mass.
Deep beneath London, the Laundry archives occupy several miles of disused subway tunnel. The shelves are crammed with documents and reports. Eyewitness statements, newspaper cuttings, court transcripts, the diaries of madmen, autopsies, scientific papers, archived material – from these, the Laundry works to piece together the shape of the world. A seemingly innocuous report may contain vital information when correlated with a dozen other files. Triangulate the doctor's report about an outbreak of strange dreams with seismic activity under the Pacific, and find the traces of the sleeping god. Match the suppressed play from Shakespeare to troop movements in Syria to plot the shape of impending doom.
The Dossiers contain extracts from the murkier reaches of the Laundry's archives, a selection of unexplained encounters, unverified reports, uncorrelated data, loosely organised by whatever codeword seemed to fit. The truth exists in the unseen connections between them. The Mythos Dossiers contain dozens of reports, handouts, eyewitness accounts and deranged speculation about the horrors of the Mythos. Read them at your peril.
Some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the light into the peace and safety of a new dark age...