For decades a shortwave numbers station broadcast five-figure groups to no one — until the night it answered back. Signals archivist Gordon Selby plays the recordings, traces the carrier to a transmitter that shouldn't exist, and asks what happens when a dead frequency starts responding to the people listening.

Tonight's Numbers Station Puzzler: crack the broadcast, then email your answer and the episode number (episode 51) to [email protected] for a shot at a secret line to the show.

Presented by Double Secret Labs — we do science so you don't have to.

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