In the year 5124, the Tengri system is the farthest-flung and most isolated of Earth's six colonies. With the distance from their nearest neighbor measured in centuries, Tengrans have spent more than two thousand years in safe isolation, terraforming the system's hostile planet and engineering soaring orbital habitats to fill the space above it.

Until a routine calibration procedure in one of the Space Traffic Control cameras turns up a star where no star should be.

Nikolai Ogorodov, senior-most captain in Tengri's tiny Navy, is facing the grim prospect that he could retire still waiting for something actually exciting to happen, when word comes in that Traffic Control has spotted the deceleration flare of a ship's drive. It's a ship – and a drive – unlike anything Tengri has seen before, and Nikolai is dispatched to determine if the newcomers are a threat to the long-standing peace.

Urthe Agajanian is an under-funded and over-caffeinated young researcher on Orbital Island Peridot. With the Tengri system sporting only the barest, tantalizing remnants of a long-departed alien presence, it's hardly surprising that Urthe is possibly the system's only working xeno-technologist. When a ship turns up with a delegation claiming to be actual aliens, come to trade technology with humanity, Urthe's obscure specialty is suddenly, spectacularly relevant.

Urthe and Nik approach the situation from vastly different backgrounds, each holding a different, incomplete picture of the crisis facing their home. Yet they will both find themselves making decisions that could impact the survival not just of Tengri but of humanity.