Criminal Minds Criminal Minds

Criminal Minds executive producer Erica Messer knew very early this season that she wanted to do something out of the ordinary for the season finale.

Finale Preview: Get scoop on 39 must-watch season-enders

"I wanted to ground it with our team and I wanted to end with the idea that good things happen to good people," Messer tells "Our team puts up with all this crap from horrible people all year long, so let's actually celebrate them. We see so many bad images all season long, can't we just have our heroes be happy and smiling and dancing? We knew early on there would be a wedding at the end, not an SUV explosion [like in the Season 3 finale]."

Then in February, Messer learned that longtime cast member Paget Brewster had opted to not renew her contract and would once again be leaving the show. (Brewster departed last season to shoot a comedy pilot, but returned when it wasn't ordered to series.) "We thought, 'How do we keep the spirit of the finale alive — ending on a happy note — given this sad news?'" Messer says. "But I think it mirrors real life. At almost any wedding, you can find somebody who's sad because their partner isn't there to see it or there's a grandparent who died and wasn't there. There's always a bittersweet element at weddings."

But how bittersweet will it be? While some writers suggested killing off Brewster's character, Agent Emily Prentiss, Messer held firm to her happy ending.

Paget Brewster to exit Criminal Minds at the end of the season

"We've already had Prentiss' [fake] funeral. We already played that game," Messer says. "I didn't think it was fair to everybody left behind to now have to mourn the death of her for real. It seemed repetitive and it also seemed cruel. That was off the table immediately as far as I was concerned. [We wanted] to be able to cry for the right reason at the end of the season."

Before she leaves, however, Prentiss and the rest of Behavioral Analysis Unit will have to contend with Izzy Rogers (Battlestar Galactica's Tricia Helfer), the leader of a bank-robbing gang who has taken hostages in D.C.

"She's like the evil version of Prentiss," Messer says of Helfer's character. "She has international ties and she did some really bad stuff. She has aliases and the whole nine yards, just like Prentiss did when she was undercover. But Prentiss was doing it for good. Immediately, she is the antithesis to Prentiss."

Criminal Minds Exclusive: American Graffiti's Candy Clark to play JJ's mom

Although the BAU is initially called in because the crisis negotiation unit is otherwise occupied, it soon becomes clear that our team of heroes are the perfect people for the job. "Ultimately, she is a serial killer masquerading as a bank robber," Messer says. "Our team comes in because the behavior suggests they do this every month — they kill somebody for the fun of it, not because they're in the way. The woman's off her rocker. She's just a bad egg."

Ultimately, one of the team members will risk everything by entering the bank and trying to talk Helfer's character down. But fear not — we're pretty confident everyone makes it to the wedding — including a cavalcade of familiar faces, such as JJ's beau Will (Josh Stewart) and a returning Strauss (Jayne Atkinson). (Also, if you're still wondering who is getting married, here's a pretty big clue.)

Criminal Minds: Our Top 8 Prentiss moments

"We've put in nearly every character who's ever been on the show, recurring in any way," Messer says "We wanted them to have a presence. You're going to see faces you haven't seen since the Super Bowl. We wanted this to be a celebration of the seven years we've been running strong."

More than anything, Messer says she is proud the show was able to give Brewster a proper send-off (again). But she says that definitely doesn't rule out some return visits down the road.

"No one wants to see her go," Messer says. "But we respect her so much and these are her wishes — it's on her terms. And if she wants to come back and play for an episode, that's something we can do. She has a history and she's a huge part of this show. As far as we're concerned, Agent Prentiss will always be a part of this series."

Criminal Minds ' two-hour Season 7 finale airs Wednesday at 9/8c.