Reid's mother Diana is finally back on Criminal Minds -- and she's still not doing too well.

Jane Lynch returns to Criminal Minds Wednesday for the first time in more than eight years, after Reid (Matthew Gray Gubler) decides to take his schizophrenic and Alzheimer's-stricken mother out of a clinic and care for her himself. But that's easier said than done, as he relays to JJ (A.J. Cook) in our exclusive sneak peek.

Lynch's return as Diana, coupled with the continued hunt for Mr. Scratch (Bodhi Elfman), kicks off the back half of Season 12, which will feature the show's longest serialized arc yet. "I think it's going to be really surprising for everybody, and I think also incredibly rewarding to everyone who has watched as long as they have, to have a more serialized arc for our heroes to deal with," showrunner Erica Messer tells TVGuide.com. "It really all starts with [this episode]."

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Lynch was originally scheduled to appear in two episodes, but, as previously reported, will now be in "two and a half" -- with the "half" likely being the conclusion to the Reid-centric trilogy of episodes, aptly titled "Spencer," scheduled to air Feb. 15. Messer co-wrote that episode with Kirsten Vangsness, and, lest you forget, the two have previously penned some biggies: Gideon's (Mandy Patinkin) off-screen death in Season 10 and Shemar Moore's exit last season.

"This is absolutely a gigantic story for Reid," Messer says. "It's really the story of a son who is not going to give up on helping his mom. The fact that he's a genius and solves all kinds of problems and can't solve this one is sort of the heartbreak in the journey."

Criminal Minds airs Wednesday at 9/8c on CBS.

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