Meshach Taylor and Joe Mantegna Meshach Taylor and Joe Mantegna

When Joe Mantegna joined Criminal Minds in Season 3, he had two requests.

"We started talking about story lines and two things I brought up immediately were: I would like to someday explore the fact that [Rossi has] had three wives. Let's have at least one appear. And the other thing was, let's do something with his military background since he's a vet."

Criminal Minds' Jeanne Tripplehorn: I hope fans will like Alex Blake

A year after viewers met and said goodbye to his first wife Carolyn (and learned he had a son who died at birth) and five years after he joined the CBS procedural, Mantegna's last wish is finally coming true. On Wednesday's episode (9/8c, CBS), Rossi will reconnect with his former Marine Sgt. Harrison Scott (guest star Meshach Taylor) while the BAU is in Los Angeles for an unrelated case.

"I spot somebody that looks somewhat recognizable to me and it turns out to be my commanding officer from when I was in Vietnam. The next thing you know, you're looking at flashbacks of a young David Rossi," Mantegna says. "They've got these young actors playing us who are superb. It's a little departure for us as a show, but it's a fantastic departure."

But the reunion is not as simple as bumping into each other on the street and meeting up for coffee. Scott is now a homeless vet — an issue that is close to Mantegna's heart. The actor co-hosts PBS' National Memorial Day Concert every year and has been working with America Wants You!, an initiative that encourages corporate America to hire men and women returning from Iraq and Afghanistan. He and his assistant Danny Ramm pitched a story line involving homeless vets years ago, and Ramm even wrote a script. "I read it and I was like, 'This is fantastic,'" Mantegna says. "Luckily, the powers that be read it and felt the same way and were like, 'Yeah, we can make this happen.'"

Criminal Minds' Joe Mantegna: Our returning troops need jobs

"We've always wanted to do it, but the timing was never quite right and we couldn't fit it in," showrunner Erica Messer says. "But we're finally able to do it now and fans will see a side of Rossi they've never seen before — not as a profiler, but as Marine before his renowned profiling career. It's a doubly special episode for Joe and we're very proud of it."

In the flashbacks, viewers will see a 19-year-old Rossi (played by Robert Dunne) in Vietnam working under a young Scott (played by Joseph H. Johnson Jr.), and the influence Scott had on him. The episode is Rossi-centric from beginning to end, opening with the present-day crime-fighter writing another book and closing with a tie-in to that. "The thing I like most about the episode is that it still satisfies everything you want in our program, but it also takes one of our characters and goes behind the curtain and you see his past life in the military," Mantegna says. "They blend together perfectly. And Meshach's performance is going to really, really surprise people, especially people who only know him from his work on Designing Women and things like that."

Photos: Check out the most memorable TV character replacements

Now that the series is in its eighth season, Mantegna thinks it's important and necessary to delve deeper into the characters' lives beyond things like Rossi's penchant for Italian shoes and other finer things in life. "I know that I, as a viewer, want to know about these people I've been watching for so long. Our show, by its structure, tends to shy away from the personal stuff, which I understand, but I think you have to go there eventually. It's time. It's been a long time coming," he says. "I don't care if it's Mary Tyler Moore or Honeymooners, Seinfeld or whatever, but when you see flashbacks, you go, 'Oh, yes, this is a treat for us longtime fans who are not just casual watchers of the show.'"

Messer agrees and promises more personal stories this season. The show first planned to do so two years ago, but plans were derailed thanks to the casting shakeup with Paget Brewster and A.J. Cook. Besides Rossi, the show will also dig deeper into Morgan's (Shemar Moore) Chicago upbringing later this season a la Season 2's "Profiler Profiled." "It is fun to do these stories because we as writers and the actors still get to learn about these characters after eight years," she says.

8 spoilers for Criminal Minds Season 8

Rossi's military homage is a one-off episode for now, but Mantegna is just happy that the door is open for possibly more in the future. "Regardless whether there will be more or not, I'm just so thrilled that we were able to make this episode and I think it came out so wonderful," he says. "It makes a statement, it makes a point. It's beneficial in what it talks about and what it shows. Hopefully people can realize, 'Wow, [homeless veterans] is an issue and it's important.'"

So now that his wishes have been fulfilled, what does he want to happen next for Rossi?

"No more wishes. I try to keep my wishlists pretty small," Mantegna says. "My focus is to be realistic about them and to do them the best we can. I'd just like to expand upon those two things. Let's meet another wife!"

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