Change is coming to Criminal Minds. Sure, it could be said that change has happened all throughout the current 12th season, with Hotch (Thomas Gibson) no longer on the show and Derek (Shemar Moore) having been gone for almost a year now. But, according to TVLine, Erica Messer, Criminal Minds‘ showrunner, even more changes are coming to the show.

One of the first changes includes the return of Diana Reid (Jane Lynch), Spencer’s (Matthew Gray Gubler) mother who has schizophrenia and was recently diagnosed with Alzheimer’s disease, in Wednesday’s episode. This marks Lynch’s return to the show since the fourth season of the show, though she’s been mentioned repeatedly.

But the biggest change that Messer previewed is more of a serialized storyline in the back nine episodes of the season, marking one of the first times that the show has done a serialized story. “It feels like we’ve earned the right to tell some serialized stories. so we’re running with that, telling a really big arc that will last all of the back 9 (episodes) of Season 12,” Messer said.

Throughout the show’s history, there’s only really been one serialized story, which took place in season four and season five with the George Foyet (C. Thomas Howell) storyline, which culminated in the 100th episode of the show.

Messer also previewed the 13th episode of the season, “Spencer,” which was written by Kirsten Vangsness (Garcia), who wrote the episode where Moore said goodbye to the show and the death of Gideon. The episode starts “a journey for (Reid) and for the team that I would argue we never even imagined would happen — and yet it happens, and we’re along for this ride. And it’s an intense one,” Messer previewed.

Vangsness also talked about the episode, saying “I seem to co-write the episodes that change the course for people. That does not mean the ends of people, it just changes their course. So (episode 13) is a course changer.”

Messer also previewed the return of a character coming back to the show for some of the episodes, but she wouldn’t say who’s returning. “We’re really acknowledging the history of the series and being able to bring back people who have made an impact, good or bad, on our characters. And we’re having a really good time doing that,” she said.

She also added that the serialized storyline is “reenergizing” the cast and also said that the last night episodes really focus on different members of the cast because of “changes they’re all faced with.”

Criminal Minds returns Wednesday at 9 p.m. on CBS.

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