So what has Martha been up to since we last saw her in Doctor Who?
"She left the TARDIS and we don't know how much time has passed, but she is still interested in alien incursions and is now working for UNIT. She's qualified and has this important position there, so that's how she gets in touch with Captain Jack. They're both working on these unexplained deaths and she has some information that [Torchwood] don't, and vice versa, so they work together."
How did she get the job at UNIT? It's said that she was recommended by a "highly impeccable source".
"The fact that it was the Doctor? Thing is, when I go back into Doctor Who and the Doctor and Martha meet up again, they do talk about the fact that she's worked at UNIT. So it is re-iterated and explained more. But it was him that got her the job there, yeah."
What does she do there?
"Well she's a qualified medical doctor so [her job] is related to medicine but also because of her experience in the field and seeing so many things first-hand that the majority of people haven't, she gets a wider scope. She works a lot with aliens still. The world the Doctor has exposed her to is not something she is quite ready to leave behind. She can't travel with him, but she's still interested in it all."
How has she changed since we last saw her? She seems a lot more confident and knowledgable.
"One of the reasons
Does that carry through when she meets The Doctor again in series four?
"Yes, absolutely, and when they do meet again it's more in a professional capacity. She's outgrown him really. She was always mature, independent and all those things but she was still a bit wide-eyed with him. And that's what's gone. She still really respects him and knows he's far beyond her intellect and the rest of it, but she was dominated by him and now there's a different dynamic there. Ultimately they're the same people, so there's still that connection, but it's a different dynamic."
"Well, Jack has called her in, basically. A lot is left for the viewer to deduce and you don't get the impression that Jack and Martha have been in touch loads, but you do get the impression that they know how to get hold of one another. We learn at the beginning that he's called her up to come in and help with this investigation because she's got some further information that could help them solve their mystery. So she arrives to become part of the team for a bit."
Does she have the hots for Captain Jack? She seems to probe Ianto for information!
"I think it's just more of an interest really. Jack is this very sexual person and all throughout Doctor Who last year he kept flirting with her and making these innuendos but she finds him harmless and entertaining. He is a good-looking, sexy man. But I think it's playful fun. She wants to know more, they all want to know more. All of the Torchwood team are always asking each other about him, who he is and where he came from. Even Martha, after all she's been through with him, nearly coming to the end of the world together, is now trying to fill in the in-betweens and find out more about his personal life."
And does Freema have the hots for John Barrowman?
"John Barrowman's marvellous. He's a unique human being. I wish I could shrink him and keep him just for myself because he lights up a room. He's just so brilliant in every way. He works really hard but he plays really hard as well. If anybody else was singing in a makeup truck at 5 o'clock in the morning you'd want to do something to hurt them. Nobody could get away with it but John Barrowman. He puts a smile on everybody's face. I adore him!"
Do you think there is possibility for Martha to join the Torchwood team full-time in a future series?
"I would like to continue a little bit with Martha. I don't know how, or in what capacity, but I feel there is a little bit more I could do with her. I would like to stay within the family, whichever way... the door is kind of left ajar, in some ways, I guess, so we will see - but I would definitely like to stick around."
But before that you're back in Doctor Who for five episodes...
"Three in a run - four, five and six - which have a nice arc to it (four and five are a two-parter), then away again, and then back for the big finale. As I said before, you can expect a slightly different dynamic. They've still got this friendship but there's somebody else in Martha's life now so she doesn't need The Doctor in that respect. That part of her soul has been fulfilled. That attraction has dissipated and it's quite professional. It's nice to see how they've moved on, because she did feel quite strongly about him. Altogether she decided not to travel with him any more because of how she felt and it wasn't returned, so it's great to see her have moved on from that to value his friendship enough to still want him around."
Do we meet this new boyfriend at any point?
"Erm... no. You don't. He's spoken about, so you get a good picture painted of who he is."
Finally, what did you think of the Christmas special with Kylie? Was it difficult to watch, not being part of it?
"No, it wasn't weird at all, because I watched the show before I ever could have dreamt I'd be part of it. I enjoyed Doctor Who as an objective spectator, a fan, but of course when I became involved in it, you're not quite as relaxed [as a viewer] than otherwise. As soon as you see yourself pop up on screen it's like 'mental note!' So watching the Christmas Special, for me, was like going back to being this objective fan and watching it like I had. It didn't feel to me like I was thinking 'Oh I could have been there' or 'I could have done this scene'. It felt like a movie, a completely separate project.
"I imagine the same will happen for me with series four. I will watch all of it and for those [episodes] that I'm not in, I will have a very different interest to those that I am in. It's quite a disassociative interest and it was surprisingly easy to do so. I don't feel like I'm hard done-by in any way so it's not something that bothers me at all."
Torchwood airs Wednesdays at 9pm on BBC Two, with a first-look following on BBC Three straight afterwards.