Criminal Minds, CBS's second-longest-running series behind NCIS, will have a two-hour finale starting at 9 p.m. Wednesday, March 18.

The real mystery is whether the finale will be only for Season 13 or for the series itself, as CBS has continued its pattern of waiting until the last second to decide whether or not to renew the veteran procedural.

Erica Messer, executive producer, and showrunner has been with Criminal Minds since its beginning in 2005.

Previously a writer on series such as Alias, Charmed, and The O.C., Messer also served as executive producer and showrunner for the spinoff Criminal Minds: Beyond Borders for its two seasons.

Taking time out from developing programming at her Erica Messer Productions company, Messer talked all things Criminal Minds, including its finale and possible future.

Give us an overview of what’s going to happen in Wednesday’s two episodes.

I guess we'd equate it, in a sports analogy, to a doubleheader, two unrelated episodes even though they're airing as our finale for the year.

Our first hour is a really interesting story about a phenomenon called “The Hum,” specifically in Taos, N.M., where our case is for the week. It follows the story of an unsub who has been affected by the Taos Hum. Major changes in his life have happened because of it, and he is now killing.

That story wraps up nicely. We learn a little more about Tara Lewis in that episode. We see the beginnings of more of a friendship between Lewis and Luke Alves.

We see some of that friendship and lightheartedness between Tara and Luke enter into the next episode. But the rest of that episode is pretty darn serious. It ends up following the case of an FBI agent who had been missing for over a year, only to find he had been held captive by people who we believe are serial killers.

That episode unfolds and has a few surprises in it, culminating in a cliffhanger that will be surprising to many people.

To end with a cliffhanger, you must be fairly confident about a 14th season. There’s nothing that goes down worse with a viewer than a cliffhanger followed by cancellation. So how confident are you?

Well, I would love to feel more confident. I do feel like our show has been on for 13 seasons, and I would feel devastated if it ended with Episode 299, for more than just that reason. Certainly, the [cliffhanger] story itself deserves to be answered, but also I feel very hopeful we could have a 300th episode.

I would love to have an entire season to keep telling stories. I feel with the changes in the cast and the chemistry that that group has right now; it has really rejuvenated the creative process for everybody.

We have so many more stories to tell. We have so many ideas and characters, and there's always bad guys to catch. And we have a great group of good guys to do it. I'm very hopeful that we will still get to tell our stories.

There was no season-long storyline this season, unlike the Reid-in-prison one from Criminal Minds Season 12. Why did the show’s production team make the decision to avoid that this season, other than the thankfully short (Linda) Barnes arc?

We felt that there wasn't going to be anything bigger than what we did last year with Reid. He was in prison for so many episodes last year. It was an availability issue, and that was one of the reasons we went that route with the story.

Also, it was also creatively a really great challenge, writing-wise, for all of us, and acting-wise for Matthew, who had been playing Dr. Reid for so long. It was an opportunity to give that character more layers, some complications that helped Reid grow as a character.

This year, we brought in Barnes, who had appeared on Criminal Minds: Beyond Borders. Since Beyond Borders is gone now, we felt there was an opportunity to say Barnes is the reason that team, the IRT, doesn't exist anymore and she may be the reason the BAU doesn't exist.

So the stakes felt raised to us, compared to the other seasons where we'd done “the BAU may be in trouble.” It felt very real because you had Matt Simmons, Daniel Henney's character, saying, “Yeah, let me tell you a little bit about Barnes. She investigated our team, and now the IRT doesn't exist. So she will be looking to do that again here.”

That was a bit of a dance with Barnes for a few episodes. We felt a bigger threat than Reid in prison was that this team won't exist anymore. And the way to do that was to have a real threat personified by Barnes.

Some viewers have grumbled about Reid’s “sabbatical,” concerned that Matthew (Gray Gubler) may be on his way out. Any possibility of that happening?

I don't see any signs of that. In fact, he is committed to the show as much as he can be. We have to write in those things if he's not in that episode, that's all.

This season’s new character, Matt Simmons, fit in seamlessly with the team, unlike some other recent additions. Why has Matt worked out so well?

I think part of it is that Daniel has played this character for two years on Beyond Borders and he created the character on an embedded episode of Criminal Minds.

So he comes to the show with a history with the BAU. Certainly, with Garcia, there's a bond, and with some of the members of the team; he knew them. We had set up that history in the embedded episode in Season 10.

I think automatically there was a comfort level that shows on screen. Also, it helps that Daniel was saying this kind of dialogue already for a couple of seasons. His character was well established as a working dad with four kids. His wife works, they juggle everything, but they're a happy family.

Daniel brings that same thing to the show behind the camera. He's just a lovely human, and he's fit in very well with the rest of the cast.

What’s the secret to keeping a long-running series fresh?

I think we always look to challenge ourselves. The writing staff always brings amazing ideas to the table; the cast is amazing at selling some of our crazy ideas as grounded.

The secret is having a dynamic cast and keeping the ideas going in the writers' room. We also have an outstanding crew which creates the United States for us each year right here in L.A. It takes a village is what I like to say.

The finale airs 9-11 p.m., Wednesday, April 18. To catch up beforehand, watch Criminal Minds online.