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Paget Brewster joins the cast as Emily Prentiss, a new agent assigned to the Behavioral Analysis Unit. To her surprise, she has to immediately fight suspicions of nepotism (her parents are high-powered diplomats) as she was placed in the BAU without Hotch or Gideon being notifed.
Meanwhile, the team is dispatched to Saint Louis to track down two serial killers operating concurrently but independently. The killers' M.O. and victims are vastly different from one another, yet the team discovers a surprising connection.
This episode marks the first appearance of Paget Brewster as Emily Prentiss. She takes Lola Glaudini's place on the main cast.
Paget Brewster now appears in the opening titles. She has also been added to the shot of the whole cast at the end of the titles. A.J. Cook's picture in this shot has also been changed and updated with a newer picture.
Twins Sara and Hanna play the role of Katie Carroll.
Hotch: What can I do for you?
Emily: Uhh, well, I-I guess I was hoping you could tell me where to put my stuff.
Emily: I-I'm supposed to start here today at the BAU.
Hotch: There's been a mistake.
Emily: I don't think so, sir.
Hotch: There's definitely been a mistake.
Reid: When Mill Creek kills, the Hollow Man shoots another prostitute.
Morgan: So, one doesn't want to be outdone by the other? Sounds like sibling rivalry to me.
Hotch: They've been killing independently of each other for a year now.
Gideon: With each kill, they're learning something... from the other.