The Hiss is a hostile paranatural force of resonance that invaded the Oldest House on October 29, 2019, resulting in the near-destruction of the Federal Bureau of Control. Originating from an alternate dimension, the Hiss influenced FBC Director Zachariah Trench into unleashing it using the Slide Projector Object of Power. The Hiss's source of resonance was cut off by Jesse Faden when she deactivated the Projector; however, the possessed Hiss agents still lingered in the Oldest House, continuing to pose a major threat.

The Hiss originated from an alternate dimension which could be reached via one of the slides connected to the Slide Projector Object of Power from Ordinary, Wisconsin. During the Ordinary AWE, Jesse Faden burned all but one of the slides (Slidescape-36), and the Projector was contained by the FBC. Zachariah Trench kept one of the burned slides. As exploration of Slidescape-36 was carried out under the supervision of Casper Darling, Trench, attending one of the expeditions, fell under the influence of the Hiss. When Darling returned the Hedron from Slidescape-36 and began to produce HRAs, Trench, fearing Hedron would take over the entire Bureau, unleashed the Hiss upon the Oldest House on October 29, 2019. The Hiss nearly destroyed the entire Bureau, possessing its agents, the topography of the Oldest House, and numerous Altered Items and Objects of Power. An external lockdown was placed in effect, cutting off the building's sectors from one another.