I remember the first time that I heard a numbers station. I had managed to acquire an old radio, one that was capable of picking up the shortwave bands, and was turning the tuning dial this way and that. Everywhere there was the hiss of static with the occasional burst of intelligible noise as I came across a distant station. There were snatches of speech, fragments of music, and then there was silence.

Silence? I turned the dial back to the dead spot. The noise from the speakers cut out, and I listened for a moment. I was about to move on when a tinny voice spoke.

"Pay attention!"

I almost said, "Who? Me?" but I quickly stopped myself. The voice spoke again.

"Pay attention! Six. Nineteen. Twenty five. Ninety nine."

The voice spoke continuously for a minute, reeling off a string of numbers, never once repeating itself. I sat there, my face illuminated by the soft light from the radio's innards, listening in wonder. Finally the voice finished, and there was silence once more. I listened for a few minutes longer, then made a note of the frequency the radio was tuned to.

The next night, I tuned in again. The dead frequency was still there. After a few minutes of silence, the voice appeared: "Pay attention!" followed by another string of random digits. This happened every night for the next five nights, then stopped. I started searching the frequencies again, looking for the voice. Every so often I would find another dead spot and listen, but there was just silence.

A friend of mine was a radio ham. I envied his collection of equipment and aerials. I asked him if he knew about my mysterious station.

"Yes," he said. "It's what we call a numbers station. They're all over the band. They're just a nuisance."

I thanked my friend, but his answer didn't satisfy me. I needed to know more. Obviously the radio hams were the people who would know, so I started subscribing to a number of magazines. There were contributors who talked about the numbers stations - and more! There were stations that would play snatches of strange music, some that would emit pure electronic tones, and others that transmitted regular pulses of noise. I tuned in to listen to these stations, noting what I heard and when.

People speculated on their purposes. Intelligence agencies? Mind control? Weather experiments? Nobody seems to know. I learned of loop lines, EVP and other strange occurrences. The information flowed around me and through me as I tried to work out what it meant. It took months, but I eventually understood.

I can't explain it to you. I'll sound mad if I do. If you discover it for yourself, then you'll understand. All you have to do is take down this string of numbers and take it from there.

Do you have a pen and paper? Good.

Now, pay attention!