How I Met Your Mother returned for its ninth and final season this week on CBS. In last May’s finale, viewers finally met the mother, played by Cristin Milioti, who joins the cast full-time this season.

The entire season will take place on the weekend of Robin (Cobie Smulders) and Barney’s (Neil Patrick Harris) wedding with the action flashing forward to show Ted (Josh Radnor) falling in love with the long-awaited title character.

Paste recently caught up with Carter Bays, the executive producer and co-creator of How I Met Your Mother, to talk about plans for the ninth season, the casting of the mother and what to expect in the final moments of the series.

Paste : What does it feel like now that you are filming the final season?

Bays: It feels like the movie The Great Escape where we’ve been digging our tunnels and fashioning things out of stove pipes and making our fake passports and now this season we’re breaking out. This is it.

Paste : What can we expect of this season?

Bays: We’re sort of going to be alternating between crazy silliness and “hey it’s great to see that guest star again” and the highest high drama we’ve done on the show. It’s a very operatic season I think—highs and lows.

We have really exciting stuff to write about right now. We’ve never been in a place where it’s July and we’ve plotted out the entire season, but we have this year because there’s so much exciting stuff.

The mother is involved from day one, which is fun. We’re really going into this season knowing this is our last shot at it and I think what we don’t want to do is leave anything unsaid. So we’re trying to say everything. One last smorgasbord of anything you could possibly want to see on the show, you’re going to get to see this year.

Paste : How did you come to cast Cristin Milioti in the long-awaited title role of the Mother?

Bays: [Co-creator and executive producer] Craig [Thomas] saw her in Once on Broadway. I had seen her in an episode of 30 Rock and loved it. So from two different directions, we both kind of knew of this really talented performer. Our casting agent had a secret file of “if they ever ask me to cast the mother, here’s my list” and Cristin was at the top of the list.

Much like finding the actual love of one’s life, there was just an x-factor there. There was no real checklist. Cristin just kind of brought something. We couldn’t have created her on paper but when she showed up it was, “Yeah of course that’s who Ted ends up with.”

Paste : Although Cristin was nominated for a Tony for Once, she is a relatively unknown. Was important for you to not cast someone famous in the role?

Bays: For the final scene of the last season we didn’t want it to be, “Oh look it’s Jennifer love Hewitt.” No offense to Jennifer Love Hewitt, she’s great, but people already know her, and people have already decided whether they like her or not.

Paste : How will Ted’s relationship with the mother unfold?

Bays: Without giving too much away, because I like the way it unfolds, it happens in nice, surprising ways I think. We don’t want to just be “okay, now he’s met the mom, and now here’s Mad About You and here they are fighting about how he forgot to put the lid down on the toilet.” It’s not going to be that. It’s a continuation of what we’ve established for the last eight years. We’re going to see the big moments, the great moments, the happy wonderful, gooey exciting moments that Ted has deserved for all these years. There’s going to be happiness and tears, all the emotions that have gone into the show all these years just turned up to 11. It really feels like we’re going out on a crescendo.

Paste : In last March’s “The Time Travelers” episode Ted makes a speech to the unseen mother lamenting that it’s going to be 45 days until they meet and tells her “I am always going to love you. Until the end of my days… and beyond.” Some fans, including myself, took that as a hint the mother is actually dead in the future. Were you surprised by that reaction?

Bays: I was surprised. I’ll just leave it at that.

Paste : Is it crazy to think that?

Bays: Um, you know, no comment.

Paste : Okay, what’s coming up for Marshall (Jason Segel) and Lily (Alyson Hannigan) this season? When we saw them last, Lily wanted to move to Italy for work and Marshall accepted an appointment as a judge without telling Lily.

Bays: They’re headed into one of the biggest conflicts they’ve ever faced as a couple. There’s no way around that. He wants to do one thing with his life, and she wants to do something else with her life and those two things don’t line up. Marshall’s a very traditional guy in a lot of ways, and Lily is a very sort of marches to her own drummer and we’re going to see that conflict come to a head in a lot of ways. There’s not an easy solution for it and it’s going to be rough at some points but at the same time we want to really celebrate them as a couple and celebrate how happy they make each other and how great they are for each other. We’re going to leave on a high note with them.

Paste : Do you already have in your mind the final image of the series?

Bays: We’ve known what the last 15 minutes of the series is from the very beginning. It hasn’t changed fundamentally, but it’s definitely been enriched by what we’ve written between then and now. I think it will really encapsulate what we love about the show. I mean we’re not trying to do anything that’s too groundbreaking or daring. The show is a celebration of life and of love and of friendship and of living your memories. Making memories and living the kind of life that you’re really happy about down the road. And it’s all in there.