Emily Prentiss has recurring dreams, involving a serial killer who she was unable to catch. She had talked a fellow Interpol agent into going undercover to catch the guy, but the operation failed as he ended up killing her. Prentiss blames herself for the woman's death, and the dreams now haunt her.

Emily Prentiss asks Hotch to start an investigation on a killer she's been hunting (as part of Interpol). The killer travels to various places, performing copycat kills of infamous serial killers. The latest is a killing that mimics the M.O. of the Son of Sam.

Rossi, JJ and Prentiss meet up with local PD to view the crime scene where a woman was shot to death in her car.

Following up on the Son of Sam M.O. the team looks for another woman who may have been shot. The police department inform them about a woman who was shot in the leg.

The Unsub takes a bullet, coats it in his saliva and inserts it into his gun.

The police get a call about a man matching the Unsub's description at a warehouse. They and the BAU head over, but there's no one there.

A few blocks over they discover another murder scene, where a couple have been shot to death while sitting in their car.

Prentiss discovers a Rolex watch in the dead man's mouth.

The Unsub talks to a boy on a bus. He gives him a bullet.

Reid theorizes the killer is likely following the M.O. of one of the famous Chicago killers.

The Unsub shows up at a University, pretending to be a professor. He mets a student named Megan Ross.

Garcia has an image capture of the Unsub getting off of a bus in Chicago.

She identifies him as a crab fisherman named Michael Lee Peterson.

The BAU theorizes that his next spree will involve the rape and murder of eight students in their dormitories, following the M.O. of one of Richard Speck, a serial killer who was incarcerated at the same time as Peterson's father.

The FBI tweets a warning to all university coeds to be on the lookout for Peterson. Included in the tweet is his picture.

One of the students recognizes him as the guy who passed himself of as a professor. She calls in the information to the FBI. Just as she's on the phone, Peterson walks into her room and tells her to put the phone down.

Peterson forces the two girls into a third girl's room.

The BAU race to the school. Just as they arrive, they hear a gunshot. Peterson has killed one of the girls.

He points his gun at the two girls. One of them attacks him with a pair of scissors. His gun goes off, and the BAU race to the room.

They find Peterson holding a gun to the head of the girl.

Prentiss starts talking with him, reminding him that they saw each other in London.

Police cars roll up to the building. Prentiss points them out to Peterson and tells him to check outside. He does, and she shoots him dead.