Second volume of the Manifold series.
"If they existed, they would be here" - this is the Fermi paradox concerning the existence of extraterrestrials. They're not here, so therefore they do not exist.
NASA astronaut Reid Malenfant believes this is so until a Japanese researcher on the Moon discovers evidence of alien intelligence in the solar system. The researcher, Nemoto, calls them the Gaijin, and they seem to be e-mailing themselves from star to star.
Both Malenfant and Nemoto ask the same question: why now? Because suddenly, wherever telescopes point, there are signs in deep space that aliens are destroying worlds . . . And they are approaching Earth.
In the face of this onslaught from the stars, Malenfant sets out alone in a salvaged antique spacecraft to make contact with the Gaijin.