The Incendiaries is a novel about a cult at a fictional prestigious New England college called “Edwards.” Two students, Phoebe (whose birth name is Haejin, as she is half-Korean) and Will, begin dating. Will (whose father left when he was young) is from a working-class family. Phoebe is wealthy, owing to the death of her mother (in a car accident that she inadvertently caused). As a child, Phoebe was a gifted pianist, but she stopped playing when she determined that she was unable to improve upon the acclaimed composers who have preceded her.
Phoebe turns from being a fun-loving college student who routinely attends parties to a disciplined recluse who has joined a cult led by one John Leal. Leal claims to be a former Edwards student who spent time in a gulag while trying to smuggle refugees from Korea to China.
Will gets frustrated and grows distant from Phoebe as she moves out of their apartment and into the house occupied by the cult (called “Jejah”). Will nevertheless continues to do well in his classes, joins a fraternity, and takes an internship in Beijing. He tries to keep an eye on Phoebe by joining the cult himself (and he even goes with her to a pro-life march in Manhattan).
Will rapes Phoebe out of frustration, and she leaves him. Will loses track of Phoebe until, one day at a fraternity party on campus, he hears of a bombing from a fellow student. It turns out that Phoebe (with whom Will has lost touch) led several other Edwards students (and cult members) to bomb a local abortion clinic, which resulted in the deaths of several bystanders. Will complies with the investigating agents, who ultimately tell him that Phoebe was seen jumping off of a bridge, leaving a suicide note for Will. Will finishes college and works in Manhattan, but he thinks of Phoebe often and sometimes imagines that he sees her in the city.