The Monster Security Agency keeps the official treaties sealed. Monster Tamers keeps the unofficial sightings alive.

Most of our recurrence files concern beings the MSA has classified, contained, or otherwise managed. Some don't. Some live in the static and refuse to be measured.

The Signal Files are one of those — a subset of the archive concerned with intelligences that exist in the noise — frequencies, recursion, observers — and the woman who keeps hearing them. Figures who appear in photographs that should not have been able to record them, on plates that pre-date their cameras, behind doors that were never installed.

Sirena & Nex/Xen: the most documented case in the file. We have never determined whether Nex and Xen are one entity, two, or a recursion of the same intelligence across multiple instances. Sirena does not appear to mind.

When the same signal keeps finding the same woman, someone should be paying attention.