The Second Source is a working A.L. Mercer concept for FIRST SIGNAL.

Astronomers identify a repeating signal whose structure strongly suggests intelligence. Months later, a different observatory detects the same mathematical grammar from an entirely different region of the sky.

The discovery changes the question from whether there is another civilization to whether humanity has detected evidence of more than one.

The project is in scientific-premise and story development and is not yet scheduled for publication.