Calgary-raised writer Semi Chellas may have nabbed Emmy nominations for co-writing two of the year's most talked-about Mad Men episodes, but when she arrived on the set of the acclaimed drama just over a year ago she couldn't quite believe it was all real.

"It felt like Alice through the Looking Glass," Chellas said in a telephone interview Monday from Los Angeles.

"Like, I remember my first day getting taken down to visit the set and walking around just thinking: 'Oh right, it's a set.' It was always so real to me as a fan and the characters were so real to me."

Semi Chellas, rear, poses with, from left, Sonja Smits, Ilana Frank and Anne Marie LaTraverse of The Eleventh Hour in 2003. (Frank Gunn/Canadian Press)

The California-born Chellas, who moved north when her philosophy professor father was hired at the University of Calgary, has an impressive record in the Canadian TV industry. She co-created the Sonja Smits newsmagazine drama The Eleventh Hour, winning two Gemini Awards in the process, and has also penned episodes of Rookie Blue and Being Erica.

When the 43-year-old travelled to Los Angeles after The Eleventh Hour ended in 2005, she was feeling burned out from TV and had her sights set on feature work.

A shot at Mad Men

Still, that goal came with a caveat: if there was a possibility of a job on Mad Men, she wanted a shot.

And so, when there was a last-minute opening just before Season 5 began production, Chellas suddenly found herself in an interview with Mad Men creator Matt Weiner. She says she went in with a cavalier attitude, believing her chances were slim.

"I sort of thought I didn't have a chance and I almost just wanted to go to meet the people behind Mad Men," said Chellas, who has two small children — including a three-month-old baby.

"I was so thrilled coming out (of the interview) just to have met them ... and then within 72 hours I was starting there."

Now, she will compete for television's highest honour, with Emmy nods for two episodes she co-wrote with Weiner.

Both of them were doozies.

Talked-about episodes

The first is the much-discussed "Far Away Places," which featured senior ad exec Roger Sterling (John Slattery) and his soon-to-be ex-wife experimenting with LSD.

The second is "The Other Woman," in which Pete Campbell (Vincent Kartheiser) pressures office manager Joan Harris (Christina Hendricks) to sleep with a Jaguar honcho in order to land a contract. In the same episode, Peggy Olson (Elisabeth Moss) makes the life-changing decision to leave the firm. Some critics have suggested it was the best Mad Men episode ever.

Chellas says that Weiner had been eyeing the Joan storyline for awhile. But it was the parallel thread with Peggy, she says, that brought the instalment to another level.

"I think the thing that really made the episode work was the chemistry between that and the storyline for Peggy, which sort of became inevitable to us almost as we were working on the season. We started to see that Peggy was going to have to move on somehow ... and take her career in her hands and figure out what she wanted to do with it."

Collaborative process

Chellas says Weiner comes in at the outset of the season and outlines the year's broad strokes, including "the character arcs, what the era was, what year it was and what that meant to him."

After that, it becomes more of a collaborative process.

"We all had to go off and come in a few days later and pitch 10 ideas apiece and then Matt would respond to every pitch and riff on it," she said.

"All the writers and Matt do the outlines for every episode together and then you do not know if you will end up writing that episode until the outline is completely finished."

Like other rabid Mad Men fans, Chellas says she was blown away by the show's attention to detail.

"All the mail on the desks is actually addressed to Sterling Cooper and is postmarked with the date," she said. "But then there's a whole wall missing because it's a set. I really just felt like a child in some kind of Narnia situation."

Even the weather is right

Attention is even paid, she said, to what the weather was like on a particular day. She points to one episode in which Don Draper (Jon Hamm) comes to work and the shoulders of his rain coat are a little wet.

"There's no other reference to that, but it was raining in New York that week," she said. "I'm a research nerd and I love that kind of thing."

With a leading 17 nominations going into the Emmy Awards on Sept. 23, Mad Men has a chance to set a record as the most-honoured drama in television history.

Chellas was initially shocked by the Emmy nominations, but says it's all starting to hit her — along with the realization that she will have to find something to wear.

"I'm still stunned that I work on Mad Men," she said.

"I guess the news is starting to sink in because someone told me you have to book a hair appointment for that day. You're probably too late already," she said.

"It's totally daunting. Everyone is like, what are you going to wear? And I'm like, I literally don't know what I'm going to wear tomorrow!"