It tells the story of Dyhianna Selei (Dehya), the Ruby Pharaoh of the Skolian Imperialate, as she strives to reform her government and reunite her family in the aftermath of a devastating interstellar war.

Spherical Harmonic takes place following the Radiance War, a conflict fought between the Imperialate and the Eubian Concord, an empire ruled by a rigid caste of narcissists called Aristos.

Just prior to the opening scene of Spherical Harmonic, Dyhianna Selei escapes a Eubian military force by stepping into a Lock, a singularity that defines the boundary between two universes.

Her plan to go to Earth and free members of the Ruby Dynasty being held captive there, including Roca, her sister and heir, meets little enthusiasm among her top officers, as it can be seen as an act of war.

The novel Spherical Harmonic overlaps with Ascendant Sun which tells the events after the Radiance War from the point of view of new Skolian Imperator Kelric.

It also overlaps with the book The Moon's Shadow which centers on Eubian Emperor Jaibriol III and his efforts to initiate peace talks with Skolians after the war.