Both a sophisticated and ultimately disposable piece of spycraft, and the name of the profession of the people who use them.
A class of cybernetic prosthetics worn over the face
A strange mask containing a merciless demon, a parasite on those around it.
The party is walking through the forest at night when they come upon a clearing. Half a dozen black-robed corpses lie scattered across the ground, and a pentagram of blood is shoddily drawn in the dirt.
It seems these people summoned something they could not control. Whether or not the demon returns is up to the GM, but it would be just as rich if the demon never returned, and for the rest of the night, every stray sound or odd shadow will be jumped at!