The Dusk File was a plot device in A Midnight Grey, created by member The Original Munki. It consisted of information on the Dusk extracted from one of their oldest members, Aktamu, who had been captured by the Dawn. Mostly this was taken through the use of drugs and telepathy, though some torture was used just for the heck of it.
The Dusk File contained info on the Dusk's members, exploits, past and present bases, basically everything about them at the time when Aktamu was captured. A copy of the Dusk File is held by every ranking officer of the Dawn, and it is believed that it may be the key to ending the war.
In actuality, the Dusk File was not used very often, and pretty much everyone forgot about it. Oh, well. It was a cool idea.