Arcturus Defense SIGINT monitoring station Echo-7 has been tracking an anomalous radio signal designated MIDNIGHT FREQUENCY since its first detection on July 14, 2199. The signal broadcasts on a frequency of 1420.405 MHz — the hydrogen line, the emission frequency of neutral hydrogen and one of the most monitored frequencies in radio astronomy due to its significance in the search for extraterrestrial intelligence.

The signal originates from within GLMZ. Triangulation places the source somewhere in the Underworld, between levels B45 and B55, in a sector that has been structurally collapsed and inaccessible since 2178. The signal is modulated — it carries information. The modulation scheme does not match any known communication protocol, encryption standard, or data format used by any human organization, corporation, or government in our database.

Decryption efforts have been ongoing for three months. The signal does not respond to any known cryptanalytic technique because it does not appear to be encrypted. The modulation is consistent, structured, and appears to follow rules — but the rules are not human rules. The information theory metrics (entropy, redundancy, compressibility) are consistent with natural language — but not any natural language ever documented. The signal has the mathematical signature of communication without being any communication we can read.

The signal transmits continuously. It does not respond to attempts at communication — Arcturus has transmitted probe signals on the same frequency from multiple locations, with no change in the source signal's behavior. It is not a beacon (those repeat). It is not a data dump (those end). It is not a jammer (those are broadband). It is, as far as our analysts can determine, a monologue. Something in the collapsed depths of the Underworld is broadcasting a continuous message to anyone who can listen, in a language no one can understand.

Arcturus has not shared this finding with other corponations or with municipal authorities. The potential military applications of an unknown communication technology are significant. The potential implications of a non-human intelligence operating beneath the city are — in the words of the division chief — "above my pay grade and below my comfort level."