Admiral Kurt Vickers is on fleet maneuvers in the Newton System when a heavily damaged Earth light cruiser appears. The captain tells a horrific story. Earth has been invaded, and the defensive fleets in orbit have been annihilated. For decades, humans have been exploring farther and farther away from Earth and Newton searching for signs of intelligent life. Now that intelligent life has found them, it comes as an invader.

The Ruhar hit us on Columbus Day. There we were, innocently drifting along the cosmos on our little blue marble, like the Native Americans in 1492. Over the horizon came ships of a technologically advanced, aggressive culture, and BAM! There went the good old days, when humans got killed only by each other. So, Columbus Day. It fits. When the morning sky twinkled again, this time with Kristang starships jumping in to hammer the Ruhar, we thought we were saved.

Our universe is ruled by physics, and faster-than-light travel is not possible - until the discovery of The Flow, an extradimensional field we can access at certain points in space-time that transports us to other worlds, around other stars. Humanity flows away from Earth, into space, and in time forgets our home world and creates a new empire, the Interdependency, whose ethos requires that no one human outpost can survive without the others. It's a hedge against interstellar war - and a system of control for the rulers of the empire.

Five years ago Corin Cadence's brother entered the Serpent Spire - a colossal tower with ever-shifting rooms, traps, and monsters. Those who survive the spire's trials return home with an attunement: a mark granting the bearer magical powers. According to legend, those few who reach the top of the tower will be granted a boon by the spire's goddess. He never returned. Now it's Corin's turn. He's headed to the top floor, on a mission to meet the goddess.

The Hundred Worlds have withstood invasion by the relentless Hok for decades. The human worlds are strong, but the Hok have the resources of a thousand planets behind them, and their fleets attack in endless waves. The long war has transformed the Hundred Worlds into heavily fortified star systems. Their economies are geared for military output, and they raise specialized soldiers to save our species. Assault Captain Derek Straker is one such man among many.