It wouldn't be an exaggeration to say there is a lot happening on Criminal Minds this season.

Season 12 was already going to be busy, what with the addition of Adam Rodriguez's new character, Luke Alvez; the hunt for 13 unsubs who broke out of prison in the Season 11 finale; the promotion of Aisha Tyler to series regular; and the (at the time temporary) return of Prentiss (Paget Brewster). That was all before news broke last month of Thomas Gibson's suspension and ultimately immediate dismissal from the show after an on-set altercation with a producer/writer.

So how will Hotch be written out? Which unsubs are still on the loose? What brings Prentiss back for good? How will Alvez fit in? Here's everything you need to know about Season 12.

Criminal Minds: Meet Luke Alvez

1. Hotch's exit
This is the biggest question since Gibson was let go last month. He was already scheduled to be MIA in two episodes, starting with Episode 3, for his initial suspension. As we reported, that absence will be explained by Hotch going on a temporary assignment, paving the way for Prentiss to return to help out.

The show is keeping the reasons for Hotch's ultimate off-screen exit under wraps for now, but don't be surprised if the cumulative toll of the job and family demands causes him to press pause (and it certainly would be the easiest and most logical explanation, rather than, say, death — the show doesn't like killing off its main characters anyway). Hotch was SWATed in front of his son Jack (Cade Owen) in last season's finale, which would make for a plausible exit if he wants to focus on raising Jack and keeping him out of those situations again. Messer also told TVGuide.com before Gibson's dismissal that her plan at the time was for Hotch's father-in-law, Roy (Ed Asner), who has Alzheimer's, to take a turn for the worst.

"He's going to be struggling a little bit with things that are going on at home," she says. "Ed Asner's [character is] not doing too great and Jack's definitely affected by that. Losing one more person in his life is a big deal, so he'll definitely have to focus on that."

Exclusive Criminal Minds sneak peek: Garcia is so not into Alvez

2. Introducing Luke Alvez
The BAU's newest agent joins the team in the premiere to hunt the Crimson King, one of the 13 unsubs who escaped in last season's finale and who paralyzed Alvez's former partner back in the day. So, yeah, he wants revenge. "[The premiere is] really an episode about introducing this new hero and how he fits into our world and why he's such a good fit, and what that means to pretty much everybody who has to embrace a new character, but especially Garcia (Kirsten Vangsness)," Messer says.

Baby girl, naturally, doesn't take to Alvez right away, but Rodriguez believes that's a good thing. "Garcia obviously has a very close relationship with Derek Morgan (Shemar Moore). She's a little salty that he's no longer there. It's good in a way because I think the audience will feel that as well," he says. "I had a similar experience on CSI: Miami [when I] left for a while. It's hard for the audience to readjust after they become so attached [to a character]. Garcia gets to feel those feelings for the audience, which is great."

For more on Alvez, click here.

3. Prentiss' return — and stay!
Brewster was initially planning to return for at least six episodes, but was promoted to series regular in the wake of Gibson's firing. "[Prentiss is] back because Hotch is on special assignment from the director, and then she sticks around," Messer says. "We are always happy to have Paget return." It's not entirely out of the realm of possibility that Prentiss decides to stay for good because of Hotch's exit — and it'd be even more awesome if she were to replace him as unit chief. Yeah, we know Rossi (Joe Mantegna) has seniority, but he seems content not being the boss man.

For the time being, get ready for what Messer describes as a "fun friendship" between Prentiss and Alvez, which starts with a classic "the person I'm talking about is standing right behind me, aren't they?" situation.

4. Gotta catch 'em all (and by "them," we mean unsubs)
The premiere will pick up in real time, having skipped over the summer, during which the BAU has caught eight of the 13 unsubs who broke out of prison.

"We didn't want Season 12 to be all about catching these 13," Messer says. "We felt like we had so many other stories to tell that are our bread-and-butter stories that we felt like making the whole season about 13 guys and gals who got away before was just going to be a little repetitive. So instead, five felt like a reasonable number. Certainly, five throughout a 22-episode season feels different enough."

Two of those five are the Crimson King and the one and only Mr. Scratch (Bodhi Elfman), the mastermind of it all. The others are TBD pending actor availability, but Frances Fisher definitely wants to return as applesauce-spewing Antonia Slade. "She was so hilarious when she left [last season]. She was like, 'I have to be one of the escaped ones! It all started during my episode!'" Messer says. "Again, actor availability, not sure what we could do there. But she's high on our list of, if we could have someone who escaped, wouldn't it be great if she were one of them?"

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5. More Dr. Lewis
Promoting Tyler to series regular was just what the doctor ordered for Messer, who wants to do some Tara-centric episodes this season. "I love Tara Lewis so much and I certainly love Aisha," she says. "I'd love to dive into what makes her tick more. She has a big moment in the premiere episode as well."

Exclusive: Jane Lynch is returning to Criminal Minds

6. Jane Lynch's long-awaited return
As previously reported, Lynch will return as Reid's (Matthew Gray Gubler) schizophrenic mom Diana, who now has onset dementia, for two episodes after eight seemingly interminable years. In the premiere, Reid will reference their summer trip to Paris, which was initially mentioned in last season's finale. The arc for her return, which begins in Episode 11, is a "heavy Reid story" that will be very "challenging" for him, Messer teases. Need we remind you that Diana now has onset dementia?

7. Home lives
Rossi and Hayden (Sheryl Lee Ralph) are still going strong and the plan is to keep it that way. "Prentiss asks about that in Episode 3 when she sees him and he confirms everything's going well and it's all good," Messer says. "Maybe later this season we'll bring Hayden back and maybe [their daughter] Joy (Amber Stevens West) too."

JJ (A.J. Cook) and Will (Josh Stewart) are doing well, too, and will be the focus of the second episode, when JJ has a tough time coping with the abduction of two children during a case. "It's really a reflective episode for JJ and another great story of a working parent," Messer says.

8. Lucky No. 13
No, not Season 13. Episode 13 is set to be a biggie — and will be written by Messer and Vangsness, who co-wrote Season 10's "Nelson's Sparrow," in which Gideon (Mandy Patinkin) died off-screen, as well as Moore's exit last season. "The thing that's always tricky is moving pieces — is that the episode we think it's going to be or is it going to move?" Messer says. "I always feel like when Kirsten and I team up, we do big episodes, so hopefully we'll get the opportunity to do that again."

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

(Full disclosure: TVGuide.com is owned by CBS.)