Jennifer Morrison, Josh Radnor

Jennifer Morrison has three words for you: "I don't know."

Ever since her guest arc as Zoey on How I Met Your Mother was announced last month, the actress has, understandably, fielded the same question over and over again: "Are you the mother?"

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"It's not even that I can't say, but I just have no idea!" Morrison tells TVGuide.com. "It's always so funny because people think we have information that we don't, you know? I have no idea and I'm glad I don't know because I'd rather not have to lie about it."

What the former House star does know is that Zoey is going to be a "very important and large part" of Ted's life. How large? Morrison is currently contracted for 13 episodes — including the season finale that will feature a wedding — which would eclipse the nine-episode output of Sarah Chalke, who played the last important gal in Ted's life, his ex-fiancée Stella.

But it's not going to be all romance all time — or even initially — between Zoey and Ted (Josh Radnor) during Morrison's run. An activist, Zoey meets Ted in Monday's episode, and they get along swimmingly until she learns that he's slated to design the new Goliath National Bank headquarters in the place of a historic landmark she's trying to preserve.

"She definitely is someone who at the outset is very much in conflict with him, which is great," Morrison says. "But they do hit it off right away. The core of her being is passion. She's an activist, so whatever she's fighting for, she's researched it. She knows all the architecture terms, which of course is very exciting to Ted since he's an architect. Someone finally understands and cares about what he's talking about! Then it turns out they're on opposite sides!"

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By the next episode, it's time to battle. After Ted accuses Zoey of not knowing anything about architecture, she signs up for his class. "So now I'm harassing him in his classroom," says Morrison, who has shot two episodes and is currently filming the TV movie Outpost for Hope in Vancouver. "I haven't even discovered what the romance is between us because they haven't gotten there yet. It'll be interesting to see how the amount of conflict we're in now actually translates into falling in love with each other. But I think some of the greatest romances are born out of conflict."

The discord sets Zoey apart from Ted's former flames, Morrison says. More importantly, our sometimes pretentious protagonist needs to be knocked down a peg or two.

"It's time someone stick it to him a little bit!" Morrison, 31, says. "I like that they're playing a chess game. Just as much as he needs someone to shake him up, I think she needs the same — someone who is that passionate, that overly well-read on issues they fight for, to stand up to you and call you out on your stuff too. What comes out is that fun banter. It's like the old comedies with [Katharine] Hepburn and [Spencer] Tracy that have that quick back-and-forth. They're challenging each other because they're attracted to each other."

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There is another obstacle in the way: Zoey is still married to The Captain (Kyle McLachlan), who will make his first appearance in November. Morrison will work with McLachlan and the rest of the Mother gang after she wraps Outpost for Hope. "My scenes have all been with Josh so far, who's amazing. He's so talented, so smart. You show up to work and are like, 'You make my job so easy!' But I can't wait to see how Zoey will relate to everyone else," she says. "The nice thing about comedy is you get to see everybody at the table read and get to know them even though you may not have scenes with them. They're all so great."

A self-professed Mother fanatic, Morrison, who is currently not scheduled to return to House this year, campaigned for the role as soon as she heard rumblings about a possible big female character. Now, she feels like a "nerdy fan" on set with the "greatest job in the world." (As she notes, you can't beat sitcom hours.)

So how would she feel if Zoey does turn out to be the titular mother?

"Oh God, I can't even think about that!" she says. "Honestly, I'm just happy to be part of it. I think [creators/executive producers Carter Bays and Craig Thomas] have done such an awesome job of keeping the show amazing and funny. There's no way in the world I could possibly think of something funnier or better. Even if she's not the mother, I think Ted has met his match."