Inspired by this: http://en.wikipedia.org/wiki/Numbers_station
The signal comes through short wave radio, never the same frequency and never the same time of day. It always starts the same, "Attention patriots! This is Parsifal. Your transmission for the day follows." The voice is of an elderly man, the dialog in English with a noticeable Germanic accent. Once the opening speech finishes a second voice cuts in, a female voice reading off a string of numbers. Sometimes one digit at a time, sometimes rapid strings of numbers. The cadence suggests that the voice is produced mechanically, but it possesses a strange warmth and familiarity to the average listener. After half an hour the first voice starts in again, "Your transmission is complete. This is Parsifal signing off. Victory!" Fourteen hours later somewhere in Europe an agent is killed. No organization claims credit and the victim is never someone that a government can ever admit to employing. The signal originates from somewhere within the Alps, most likely the French side. All previous efforts at triangulation have failed.
You and your team are activated as of 0800 Greenwich. Money will be supplied through the usual channels, weapons and equipment must be acquired in field as per normal. Maps, documentation and radio transcripts have been left in the London dead drop. Locate source of Parsifal transmissions. Acquire code books. Locate command structure of Parsifal operation and terminate same.