For the Sojourn's initial mission, the Haraken explorer ship undertakes the investigation of Celus-5, a world identified by Willem, a SADE (self-aware digital entity), and his team of scientists, as the best prospect for a new colony.

What should be a routine survey mission becomes a disaster. To the Harakens' surprise, they discover, not one, but two alien species engaged in conflict. One of the entities, the Dischnya, hides their nests underground, and each nest owes its allegiance to a queen. On the grassy plains, where the Dischnya live, the resources are scarce, and the alien warriors compete fiercely to protect their nests. The ceena, the other species, shelter their people far away from the Dischnya, who hunt them.

Unfortunately, the Harakens' landing party is late in discovering the Dischnya's hidden nests. A shuttle and some of its crew, including Teague, Alex Racine's son, are captured by the dog-like warriors of the Tawas Soma nest. The mission is soon mired in a standoff, and Captain Asu Azasdau fires off a comm to Haraken, pleading for a rescue from Tomas Monti, the Haraken president, and Alex Racine.

The survey group might have been forgiven for their hasty landing. They were focused on investigating three objects buried in the sands along the continent's shoreline. Smooth, dark, and silver, they're ships belonging to the nemesis of every human and alien civilization - the Nua'll.

The dark travelers present a clue as to the direction of the Nua'll home world, but they also invoke a question: Where are the Swei Swee, the six-legged, whistling aliens, who once were aboard the dark travelers?