JJ arrives home after an exhausting case. She gets in a fight with her husband over not calling her about their son being sick. He correctly surmised that her case involved children.
She keeps flashing back to the events of the case. She tells her husband Will about the details, at his insistence that she get the trauma out of her system. The squad gets re-routed on a flight back from Seattle to hunt for a serial child abductor in Los Angeles, who is kidnapping sets of one boy and one girl, then eventually burning them. The BAU members are frustrated because they're getting nowhere in their investigation.
Her reminiscence is interrupted by her son's croupy cough, which reminds her of the cough of a girl, Francesa, caught in a burning building. She resumed her story, telling how the sadistic pyromaniac was accelerating his MO. She tells of struggling to interview Francesca's mother and little brother Berto.
The team settled on a pattern of older sister and younger brother for the arsonist, and the girl's younger brother was kidnapped right after JJ and Luke left. They pinpoint an unsub, John David Bates, who has an older sister that he had tried to kill with fire when he was younger and works in a fire-related profession. They determine that rejection by his sister was the trigger that set him off.
They track Berto's cel phone to find an empty van, just as a nearby warehouse bursts into flame. JJ reacts and rushes in, to find not just the missing siblings but Tricia Bates, the older sister of the arsonist. JJ sends Luke after Bates while JJ frees Trisha Bates and Berto, but Francesca is killed in the explosion. JJ blames herself for the girl's death, because Berto reminded her of her son Henry and she freed him first. Will tries to get her to see that it wasn't her fault.