Hugh McElroy, a hostage negotiator in Jackson, MS is raising his teenage daughter, Wren alone. She is uncomfortable talking to her father about sex so she asks her Aunt Bex, with whom she's close, to take her to the Center to get birth control. Not that she's having relations yet, she wants to be prepared if she chooses to go "all the way."
Wren insists Bex keep this is a secret, knowing her dad would go ballistic and lecture her. Needless to say, Wren and Bex arrive at the facility which is known for performing abortions. Protestors try to stop them, but they are ignored.
A madman unexpectedly decides this is his day to take vengeance on the clinic and brandishes his gun killing the owner and wounding others. After Bex is shot, not fatally, Olive, an older patient grabs Wren to escape to a supply closet.
Their luck is short lived as this man—George Goddard, with a score to settle—has an employee search the building for other occupants, thus, Olive and Wren are dragged into the waiting room with the others.
Hugh is on the scene to negotiate with George, not revealing to his colleagues that his sister and daughter are hostages. Wren texts him until her cell dies, but she believes her dad will rescue them.
The controversial topic of abortion is given profound insight with different characters offering their perspective. A Spark of Light commences with the conclusion of the crime relating to the day's beginning. This unusual concept of writing the novel backward in time allows the reader to attain a riveting, in-depth look into the characters' feelings, beliefs, and actions.