As the BAU members go through therapy to deal with the loss of Emily Prentiss, a woman awakens from a bad dream and heads over to a gun store. When she discovers that there is a waiting period before she is able to obtain her weapon, she grabs a revolver, shoots everyone in the store, and flees. Apparently the date is very important to the woman, and she couldn't wait the three days to get her gun.
The woman wanders the city, seemingly pretending she has a child with her. She seems especially focused on little boys. At a mall, she aids a boy after he trips and falls. When a guard approaches her, the woman flashes back to another unpleasant memory and she shoots the guard.
Reid suggests that since there is no systematic choosing of the woman's victims, the woman must be acting on emotion. Something must have deeply affected her, something like the loss of someone she loved. The team thinks that she's going after first-responders because she feels let down by them. Meanwhile, the woman tracks down her ex-husband.
Since today's date seems important to the woman, Garcia starts to research accidents that occurred on the date. She uncovers a car accident in which the woman's car was involved in the aftermath of a car chase. Her son had died and the date also happens to be his birthday. However, a police officer also died in the chase, and the media focused on his death rather than on the little boy.
The team heads for the woman's husband's home, but he's not there. They go to the woman's house and find all the mirrors broken. She can't stand to face herself, which implies guilt for her son's death.
The woman and her husband are at their son's favorite fast food restaurant to celebrate his birthday. Don wants to move on, but the woman can't let go just yet. She snaps when she hears "Happy Birthday" being sung to another boy in the restaurant.
Hotch goes into the restaurant without any protection and manages to talk to the woman. He reminds her that killing other people won't bring her son back. The woman breaks down, saying the last thing that happened before the crash was that her son was kicking her seat and she turned around to tell him to stop doing that. If she had paid attention to what was around her instead of berating her son, he may have survived. Hotch calms the woman down enough to allow her ex-husband to take the gun from her.
Morgan wonders whether Emily would still be alive if he'd gotten to her sooner, and, as he doesn't see Hotch grieving, he wonders how Hotch can go on like this. Hotch confesses that he misses Emily, just like everyone else on the team does.