Mark Sheppard does appear in the two-part premiere of “Doctor Who,” called “The Impossible Astronaut,” premiering at 8 p.m. April 23 on BBC America.

Getting much more than that out of the actor proved an impossible mission.

“Doctor what? Who’s Who?” Sheppard joked during our chat at the Chicago Comic and Entertainment Expo, before he peppered me with questions about Season 6 of the popular series. “What do you know thus far? What’s my character’s name? What do you want to know?”

We want to know everything! Here’s what we do know and what Sheppard confirmed: He plays Canton Everett Delaware III, a man who has something to do with the FBI circa 1969. He meets the Doctor (Matt Smith) and his companions Amy (Karen Gillan) and Rory (Arthur Darvill) when they travel to America on a secret mission that takes them from Utah to the White House.

As you can see from the extended trailers (click the RELATED link at left), our heroes clash with a lot of scary baddies.

“Steven is going to be responsible for a lot of childrens' sleepless nights, I think, and adults’ sleepless nights,” Sheppard said. “But what an experience, what an amazing experience.”

“The Impossible Astronaut,” which was written by “Who” boss Steven Moffatt and directed by Toby Haynes, was partly filmed in the U.S.—the first time “Doctor Who” has shot in the States.

But Sheppard filmed his work in Cardiff, Wales. It was his first time working in British TV, he said, even though he’s appeared in U.S. shows from “Battlestar Galactica” to “Leverage” to “Supernatural.”

Sheppard had nothing but good to say about the crew in Cardiff, as well as stars Gillan, Darvill and Smith.

“Matt is amazing. Matt is an extraordinary entity…,” Sheppard said, adding his take on the Doctor, which provides his only hint at what we might expect from his own character, Canton.

“There is a thing about the Doctor as a character—as Canton has to kind of experience—the Doctor is the kind of person who makes decisions for you and you kind of have to trust him,” he said. “Matt has that so brilliantly; he’s the man you want to follow. So [the question] for Canton is, is he interested in what this doctor has to say?”

So is Canton interested, I asked.

“Maybe,” Sheppard said, laughing. “I think you’re going to be more than pleasantly surprised by the scope and size and the scale of the episodes. Huge! The undertaking is huge, and as I say, the story is fantastic. Steven’s stories are always, always amazing.”

Sheppard talks more about the differences between filming TV in the U.S. and Britain, whether he spent time in the TARDIS and if, as an avowed Cubs fan, he would star in a rumored Steve Bartman movie.

Do you get to go in the TARDIS?
I’m not going to answer tha! Why would I answer that? Have I been in the TARDIS as a person? Oh, absolutely. I watched them take down Tennant’s TARDIS and I went and played in Matt’s. I watched Matt running around showing me how every single part of the TARDIS works.

Is that on a soundstage that looks kinda small, but the inside of the soundstage is really huge?
It’s bigger on the inside. [Laughs.] Cardiff is like that, actually. It’s much, much bigger on the inside.

It’s such a fabulous thing. I mean, the idea of doing “Who” and the actualities of doing it, it was just so much better than even the idea. It was such a fantastic concept. And the more I wanted to do “Doctor Who,” the better “Doctor Who” got, and the more difficult it got to be on “Doctor Who” because, I mean, [they’ve had] massive guest stars and everybody wants to be on the show, and I’m so honored to have been invited to play in that sand pit.

Right. Did you shoot all your work in the U.S., or in Cardiff?
No, no, no, I was in Cardiff. But it was fun, I’ve never shot in the English system apart from “In The Name of the Father,” a film, but I’ve never shot English television.

So at first I had a look at the call sheet and it says I’m in a scene [at] whatever time it says and we finish at 5 o’clock. I’m like, “Well, what do we do when we go into overtime?” [They] said, “Oh, we don’t do overtime.” I’m like, “Really?”

It’s tea time, right?
No, no, no. Being serious, it’s nothing to do with quaintness; it’s to do with a very different system. Because they’re, especially the unions were broken many years ago, you don’t run over, whereas American television is designed to run into overtime. It’s completed designed on how much overtime can they use, who do you have, who do you give turnaround to for the next day, who do you not do this, who do you do that. And it’s chaos, but it gets done brilliantly.

And in England, that’s been removed from them. So the chaos is how do you get it done in the allotted amount of time? It’s just as brilliantly efficient on both sides, but two very, very different systems.

So I was constantly in awe of the fact, there’s no Kraft Service table. They’re like, “We don’t do that.” And I’m like, “Well, what do you do?” So somebody will bring you a cup of tea, or I’ll go make myself a cup of tea. And they’re wonderful; they bring around trays of chocolate biscuits.

It’s just a different sensibility. Nothing is wrong with it. It’s just brilliantly different. And then by the time we went to America, I got to show them the other Kraft Service table, saying this is the way we do it. And I’m not sure it was any better.

I think it was fantastic the way that the crew in Cardiff, just wonderful people—drivers, PA’s, everybody—just fabulous, fabulous people. Everybody wanted to be there, everybody trying to make the best day we can make, knowing that we’re making great television.
You get up and go to work and it’s just a lovely place to be. It’s just fabulous. It’s just the way to do it. It’s a lovely experience.

Would you just stop and, “OK, we’ll finish the scene tomorrow morning”?
Oh, no, no, they make it work. Their time management is incredibly efficient. There are compromises, there are in everything. But there’s no waste. There’s very little waste in it.

Right.
It was just fascinating to go from one system to a completely different system, saying “How do you do that?” I was a total fish out of water, so it was a lot of fun. One system is designed to work within a particular set of rules and the other one’s designed to in another particular set of rules, and they both work incredibly well at the highest level.

I hear your dad is playing your character, Canton, when he is older?
He is?

Is that true? Or is that a rumor?
Is he?

That’s what I heard. Can you confirm or—
So April 23rd, 9 o’clock, 8 Central, on BBC America… [Note from Curt: Sheppard confirmed at WonderCon 2011 this past weekend that his father does appear.]

It’s fantastic though. Aren’t you excited that we’re actually going to see “Who” somewhat close to the time that it exists in all the countries that air it? I think BBC America is doing an amazing, an amazing job to bring this to us.

It’s really important in the world of Twitter that everything’s sort of on the same time.
Yeah, because the information breaks anyway. Coming from “Battlestar,” you go, “How the hell did we keep the last episode secret?” We shot it six months before. And some of the leaks were close to accurate, but most of it was never accurate. Which is amazing!

The Final Five, all that stuff, it’s just like incredible.
The fifth Cylon? Yeah. … [I think it worked] because people loved it; they wanted to protect it. They didn’t cheat.

You tweeted that Matt Smith is now your favorite Doctor.
Absolutely, he’s amazing. I put him up there with Tom and everybody else.

But Tom Baker was your favorite Doctor?
Right, yeah. Because I was, well, I’m 46, so he was the iconic doctor of the franchise in that way. I remember other doctors, all equally good. But Tom was really sort of it for me.
He’s a fabulous actor. I mean, truly, truly fabulous actor. You see the way he handles situations and the dialogue is just brilliant. But just his energy is exactly what I think the Doctor needs. It’s a wonderful rebirth.

David [Tennant] is David. He’s brilliant. Chris [Eccleston] was brilliant, too. The whole reimagining of the show has been fantastic. But Matt is something special. He’s really something special, and it’s great to watch him being that good … And the baddies are so scary, so scary. Did you see the Season 6 teaser?

Yes I did. It’s going to be exicting.
Exactly. It was nice to see an Ood in there. But the baddies are extraordinarily scary. Steven is going to be responsible for a lot of children’s sleepless nights, I think. And adult’s sleepless nights. But what an experience, what an amazing experience.

I love that he has both Amy and Rory are together with Doctor. It changes things up from the Doctor and a female companion.
Absolutely.

Was it fun working with the whole group?
They’re so happy and they work so hard. But they have a wonderful thing that they do, they spontaneously sing together. They would break out into song. And it doesn’t always follow form, but it’s an extraordinary compatibility that they have, that they would just break out in song, rather endearing to watch. They work so well, Toby Haynes, the director, is really, really, really good. He did “A Christmas Carol” [special] as well. He’s done a lot of the great recent episodes of “Who.”

It’s fun to be on sets with people who get it, with people who just want it to be great. And it was such a fantastic experience for me. It was just such an amazing experience. It’s better than I could have possibly imagined.

You’re perfect for a show like this, because you’ve done so many sci-fi genre roles.
Well I’m a geek.

Have you always been a fan of “Who”? Do you seek out sci-fi roles?
I’ve always been drawn to sci-fi in the context of it’s not always sci-fi. “Battlestar” isn’t just sci-fi in that way. I mean, it’s kind of a very limiting phrase.

But it’s future, past, the reimagining of history. It’s just the stories are so good, and the scope of the stories are usually so good. And the characters that I’ve been asked to play thus far have some extraordinary things to do. And it’s a great; it’s great fun. Where else do I get to be king of hell or president of the colonies?

Exactly.
I think sci-fi resonates so much with us because of the intelligence of it is what counts. And cynical sci-fi doesn’t work, cynical fantasy doesn’t work, copycat doesn’t work. Another reason why I think the first “Battlestar” didn’t work was because, nothing to do with the actors or the story or what was behind it, but it would seem to me a lot to be cashing in on “Star Wars” craze, which I think after a while we stopped those kind of things.

When we see stuff that is made from the heart, that we care about, the difference between, maybe where “Who” had ended up and where, when “Who” was reimagined, is a massive jump between those two sets of values. It takes someone like Russell [T Davies] or Steven [Moffatt] or Ron Moore to commit that much energy and effort into making something for us.

You said you were a Cubs fan. I hear there is going to be a Steve Bartman movie; would you be in it?
[Laughs.] I would love it. I’m sure it’ll be really, really good for about the first half of the movie, and then rapidly go down hill.