The actress guest-stars on Wednesday's episode (9/8c, CBS) as convicted serial killer Antonia Slade, who was put away 15 years ago by Gideon (Mandy Patinkin) -- and might now have info on two missing boys.
"She's the kind of unsub you want to bring back again and again. She reads people really well and her scenes with Dr. Reid are really pretty fascinating," showrunner Erica Messer tells TVGuide.com. "She is right on point in her reading of him and he gets thrown off."
For example: In the exclusive sneak peek above, when Reid questions Antonia in her cell she turns the tables on him and preys on his sadness over Morgan (Shemar Moore) leaving last month. Yup, dude is, understandably, still like this:
"I haven't seen it in a while, but it looks very much like grief," Antonia says. "Who'd you lose? Someone in your family? Good friend? Ahh. What's your friend's name?"
Watch the rest of the clip above to see how Reid responds. Criminal Minds airs Wednesdays at 9/8c on CBS.
(Full disclosure: TVGuide.com is owned by CBS.)