On the overnight shift at the Allen Telescope Array, Devin Marsh watches the hydrogen line and expects nothing. The pipeline flags a return as noise. Years of false alarms have taught him not to get excited, and this time he cannot look away.
By morning the noise has structure. The signal is a numbered sequence, and it comes from beyond Pluto, roughly 100 AU out, from the world astronomers have hunted for decades. Planet Nine is radiating heat and holding an atmosphere it has no business having. Someone or some thing is transmitting from it, and someone was listening.
Earth answers. Then it builds a ship.
Thirteen months of hard travel stand between the Halcyon and its destination. Commander Ray Ostrowski believes in procedure. The mission specialist believes in context. Neither one knows what to expect.
