'Criminal Minds' season 12 spoilers: A.J. Cook teases major drama affecting some fan-favorite characters

Expect to see more intense drama in the second half of "Criminal Minds" season 12.

After teasing that Spencer Reid's (Matthew Gray Gubler) mother Diana (Jane Lynch) will return in the series in episode 11 titled "Surface Tension," actress A.J. Cook revealed that there will be very explosive plot that will happen to some of the series' fan-favorite character.

"We've got some very personal stuff happening to some very loved characters, so there will be mayhem within the fandom. But don't worry, stick with us," the actress who portrays the role of JJ Jareau stated in an interview with TVLine.

Cook also revealed that her character will not be involved directly in the upcoming drama, but it does not mean that JJ will not be affected by it. "Something happens that really rocks her, indirectly. She has a hard time handling what happens," she stated.

Meanwhile, Diana's return could signify a major game changer in Reid's life. This led to speculations that the character might also depart from the Behavioral Analysis Unit (BAU) in the future of the series. If this happens, the team will lose another important member after Aaron Hotchner (Thomas Gibson) earlier in the season.

Gibson was forced to leave the show after he got involved in a physical altercation with one of the show's producer while filming the first few episodes of season 12.

On the other hand, The Futon Critic released the synopsis for the midseason premiere of "Criminal Minds" season 12. It reads: "When a bizarre hieroglyph found under a deceased homeless man's armpit is the same from previous casualties a few years ago, the BAU is called in to investigate. Also, Reid decides to take his mother out of a clinical study early to bring her home with him."

The midseason premiere episode of "Criminal Minds" season 12 is slated to air on CBS on Wednesday, Feb. 1.