When Kathryn Alexandre gives a performance in the BBC and Space Channel’s Orphan Black, it is the most intimate kind imaginable, a performance for one person.

Alexandre is the acting double for star Tatiana Maslany, who plays at least nine (and counting) roles in the Toronto-shot science fiction thriller about cloning. Alexandre has to know each character intimately, and that includes doing the different accent for each character.

“It’s incredibly personal because only Tatiana gets to see my face, so I’m playing really for her,” says Alexandre, who just turned 25.

Orphan Black Season 3, airing on Space Channel Saturdays, has become a global hit with a passionate fan base. Space just announced that it had commissioned another 10 episodes for the upcoming season 4.

Maslany, 29, has won a Television Critics Association and Canadian Screen Award for her portrayal of the different roles, which includes everything from a British con artist to a Ukranian assassin.

“The impulse is to do the character as much justice as you can,” Alexandre says. “That means speaking at the pace and mannerisms of the clone she is working with, so she can play off that. It would be difficult for her to act off a character, for example, without the accent because it’s so essential to who that character is.”

Alexandre is at the Queen St. offices of Bell Media, which owns the Space Channel. A noisy studio audience on the ground floor is being prompted to clap for daytime talk show host Marilyn Denis and her guests. Upstairs, Alexandre is in a futuristic white-themed board room that would not be out of place as the offices of executive clone and villain Rachel Duncan.

She is joined by Nick Abraham, another young actor who has joined Orphan Black’s exclusive Clone Club this year. Abraham is the acting double for star Ari Millen, who plays a militaristic clone with at least four personalities as the clone empire expands.

Abraham landed the job after Millen, a buddy from theatre school, asked him to audition. Apart from sharing roughly the same physical size, Abraham and Alexandre look nothing like their onscreen counterparts. It is perhaps acting’s loneliest job. Their role is invisible. Their range evident only in what they hope will be an elevated performance by the star. But to call them simply acting doubles is to diminish their contribution; they have to be prepared as well as any Broadway understudy.

“It can be a real challenge. We are playing brothers on the show, so you need to be on the same page,” says Abraham. “But having that connection as friends really helped from day one. It really develops a sense of trust because you have to work so closely together.”

The technical challenge in a show like Orphan Black is immense. The doubles play off the actors, and then are essentially swapped out later on a green screen. Everything shot over the shoulder is usually Abraham or Alexandre.

“When Ari explained to me what the process what about I didn’t understand what he was talking about until I arrived on set and realized how complicated it was,” says Abraham. “Fortunately, Katherine had been there before and had really broken ground and set the standard.”

And one small, but not unimportant thing: Because the doubles are sometimes the first to inhabit the roles of the clones that the stars must eventually play, their acting also influences the direction that Maslany and Millen might take when approaching the role.

“You can put a bit of what you think the character might do in the role, but really, it’s to enhance and support what Ari is doing,” says Abraham.

“We need to be prepared enough with our own tools, but it stems from what they have created,” says Alexandre.

Both Maslany and Abraham have been effusive in praise for the work of their acting doubles.

“I could cry thinking about her,” Maslany has said of Alexandre in a Screen Actor’s Guild Foundation workshop interview. “She memorizes all of my lines, all of my blocking, my mannerisms, my impulses …. and gives it back to me with a performance I can play off.”

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And normally, acting doubles don’t spark the kind of fervour with fandom that Abraham and Alexandre have. Or inspire the kind of demanding auditioning process. That’s because in one sense they are the coolest kids in the Orphan Black universe: They are the doubles of the doubles of Orphan Black. In the world of sci-fi fandom, or at least in some alternate reality, that should make them worthy of a spinoff show of their own.

“It’s really cool to see the attention the show has been getting, Ari will tweet something about us and the next thing you know you’re getting a huge bunch of followers on Twitter,” says Abraham.

Alexandre, for example after three seasons has developed her own fan base that sends her the inevitable fan art. Recently, she saw herself presented as a fairy.

“It’s really this neat relationship with fans,” Alexandre says. “From watching the show you wouldn’t know we’re there. But fans who love the show, who have delved in behind the scenes will know about us and they really love it.”

Alexandre has since moved out from behind the scenes with a role as a midwife on Season 3.

“Given the demands of just doubling it was hard to find the time, but it was great to be able to come on for a few days and play my own character, it was a different dynamic,” says Alexandre.

While the two doubles are enjoying their time on set, they say the coolest thing about being a double is living in the world of the quick change artist, changing characters several times a day.

“Definitely the coolest thing is all the costumes,” laughs Abraham.

“Yes, you wouldn’t believe how many wigs are involved, they’re a character unto themselves,” says Alexandre. “Maybe it’s all in the wigs.”