When three people implicated in murders claim that they were attacked by a "clawed shadow monster" at the moment each crime occurred, the BAU searches for a man who appears to be controlling the suspects' minds. However, as the search for the culprit continues, the life of one of the team is put in jeopardy.
- Jamie Bock - Mary Kinderman
- Andrew Borba - Tony Axelrod
- Bodhi Elfman - Peter Lewis
- Kiko Ellsworth - Daniel Karras
- Brittany Falardeau - Tabitha Merrin
- Suzanne Ford - Doctor Susannah Regan
- Thad Luckinbill - Larry Merrin
- Anessa Ramsey - Christine McNeil
- Elliott Smith - Jimmy Kinderman
- Joe Williamson - Bill Kinderman
- Aaron Hotchner: "Your memory is a monster; it summons with will of its own. You think you have a memory, but it has you." John Irving
- The name Mr. Scratch is a derivation of Old Scratch, a folk name for the devil from New England and pre-Civil War stories. Old Scratch was in turn derived from schratz, a demon of Norse mythology.
- Mr. Scratch's eerie growl was created by looping and altering the mating call of a macaw bird.
- The physical manifestation of Mr. Scratch was portrayed by Matthew Gray Gubler, while cameraman Darcy Spires cast one of its shadows for a particular scene. Drawings of "Mr. Scratch" made by the drug victims were drawn by Gubler, who made them appear different by alternating between using his right hand and his left hand.
- The surnames of the major guest characters are also names of the characters featured in the horror film The Exorcist.
- One of the unsub's murders by proxy occurred in Derry, Maine, a fictional town created by Stephen King.
- Thad Luckinbill previously costarred with Shemar Moore in the soap-opera The Young and the Restless.