The BAU is called to investigate after a woman is stabbed to death while closing up the hair salone where she works.
The woman - Jessica Randall - is the third of three murder victims which fit the same M.O.
Each victim was stabbed and the posed a week apart from each other. Each had over a dozen stab wounds, which the team interpreted as acts of rage.
The unsub changed her victims' clothes, and then washed, dried and put away the clothing in which they were killed. This behaviour indicated to the BAU that she suffered remorse after each killing.
The unsub - which the BAU determined was a woman named Ellen Connell - gets angry when her manager Sarah takes credit for her work. Later that night she goes to Sarah's home, and kills both her and her boyfriend.
At each crime scene, the BAU finds Ellen's hair, which they later determine to be indicative of her suffering from trichotillomania. She's pulling out her hair as a way of relieving stress.
After the team realizes who the unsub is, they research her history and discover that she had been in a car accident where she hit two girls - one of whom ended up dead, and the other paralyzed. They also discover that she suffered brain damage - specifically her frontal lobe, which governs her ability to control her impulses. As a result, that ability is now gone, and she reacts to negative situations with murder when enraged, only to be remorseful when she's calm again.
When Ellen's husband confronts her about her abnormal behavior, she confesses to killing her boss, among others. When he goes to call the police, she stabs him.
Her daughter Sky comes home and, when she sees her mother next to her dead father, trying to clean the floor, she panics. Ellen jumps up, grabs her and forces her to go with her.
They drive to the home of Ellen's paraplegic accident victim. Ellen screams at the girl and waves a knife in her face, demanding that she take responsibility for ruining her life.
The BAU manage to get to the girl's house in time to stop her from killing the girl. Ellen grabs her daughter and threatens her with the knife, but the BAU talk her down. She drops the knife and is taken into custody.
The other story in this episode involves Rossi, who has been followed by a mysterious woman. At first, he thinks she's a fan and is worried that she's going to invade his privacy.
When she shows up at his workplace, he calls security to have her removed. He stops when she blurts out that she's his daughter.
After Rossi is called away to deal with the case, his daughter Joy decides to go back home.
Rossi asks Garcia to hunt her down, and that's when he finds out she's on her way to the airport.
He meets her there, and explains the circumstances around his summer romance with Joy's mother, who at the time was a diplomat living in Paris. Rossi was on his way up in the FBI and couldn't stay with her.
She got pregnant with his child but never told him, because she knew he wasn't ready to have a family.
Rossi urges Joy to stay around for a while, but she tells him she needs to go - and that his grandson Ky (who is two years old) is running a fever. She says he would like the man she married, because he too is Italian.
Rossi asks if he could stay with them for the weekend so that he could meet his grandson and son-in-law, and get to know them. Joy agrees.