It is the first book in the five-volume[1] Lightbringer Series and follows Gavin Guile, known as the 'Prism' and the most powerful person in the world,[2] as he combats an uprising led by a self-proclaimed king.
The book is described by the author as "a story of normal brothers—who happen to be in extraordinary circumstances" and explores themes of conflict, resentment, and love.
The Black Prism is set in a pre-industrial fantasy world that is more advanced than most, featuring gunpowder weapons and widespread use of simple machines like pulleys and gears.
The Chromeria serves as both the governing body and the center for education and regulation of color magic, which is a central element of the series.
The Prism's abilities, ceremonial authority, status, and Chromeria-sponsored protection grant him a great deal of personal agency, though he has the least official governing power during peacetime.
Gavin, the elder brother, was groomed from a young age to become the Prism by their father, Andross Guile, who is a high-ranking member of the Chromeria, representing one of the spectrum colors.
The trouble begins when Dazen burns down the powerful White Oak family house, killing several women and children inside.
Sixteen years after the war, the Prism receives a note from a woman claiming to be "Lina," informing him of his 15-year-old son in Tyrea—a child he had been unaware of until now.
This son was conceived while Gavin was engaged to Karris White Oak, a member of his Blackguard, the most elite military force in the world.
However, he decides to bring Karris to Garriston himself before she can read the note, using a method of transportation no one else believes possible: magically-aided flight across the ocean.
As they approach their destination, Karris notices smoke and directs them to the former town of Rekton, which has been burned to the ground by Tyrean soldiers.
King Garadul plans to lead his largely conscripted army to seize Garriston and, from there, break the Chromeria's control over the world.
The box contains a white dagger that Kip's dying mother gave him, making him promise—amidst curses and abuse—to kill the man responsible for her suffering.
Gavin then enters a hidden prison within the Chromeria, where his brother is secretly imprisoned in a cell where only blue luxin can be drafted.
When Dazen mentions the box that Garadul took from Kip, Andross immediately inquires if it contains "the white luxin," a supposedly mythical substance.
Omnichrome exploits Liv's disgust with the Prism and the Chromeria to persuade her to join his cause in exchange for aiding Kip and Karris.
Inside, Kip finds a note from his mother instructing him to kill "the man who raped me, Gavin Guile," and telling him that she loves him.