I hurried into Bridgewater Studios, with a minute or two to spare. There had been problems on the underground, and a journey that I'd thought might take 20 minutes had in fact taken me the better part of an hour. There went my quiet time sitting outside having a final script read-through. Damn it.

The receptionist looked up at me at the sound of the automatic door.

"Good afternoon. How can I help?"

"Hi." I responded, still slightly out of breathe. "I have an appointment with Steven Moffat at 2pm?"

"Ah, let me just see if they are ready for you."

I leant against the counter, breathing deeply, trying to catch my breath, while the receptionist made a phone call.

"Mr Moffat? I have your 2 O'Clock here? Of course."

She put the phone down and looked up at me with a smile. "They're waiting for you. First floor, 3rd door on the right."

"Thank you."

Still attempting to breathe deeply I headed for the stairs and went up. To my slight surprise, all the offices along the corridor were walled with that frosted glass, which made everyone inside look like slightly creepy spirit people. When I got to the third door, I paused and looked through the glass. There were at least 4 black shapes inside. Oh god.

I knocked on the door, and upon hearing a man's voice call out "Come in!" I pushed the door open and went in.

Right away, there were familiar faces. I recognised Steven Moffat and Mark Gatiss straight away, having seen them do various interviews and things on the telly before. I knew Mark Gatiss did some acting work as well, but I couldn't put my finger on anything I'd seen him in.

Then I took a look at the third man in the room. He didn't immediately look at me, he was engaged in conversation with an older woman sat on his right, who I didn't recognise at all. But when he heard the door shut behind me, he looked up and smiled. It was Benedict Cumberbatch who I'd seen in various things before. But he looked different to the last thing I'd seen of his. His hair was a different colour for one, today an almost gingery auburn. And his outfit was scruffy… No, not scruffy, but casual. Jeans and a simple white t-shirt. Normally when I see him, he looks super put together and posh-boy-Brit.

"Hello." I say, smiling around the room at the four expectant faces before me. That's a little trick I learnt at drama school. Always try and be the first one to speak in an audition, then you, psychologically at least, always lead the discussion. It always sounded like bollocks to me, but the strategy hasn't failed me yet.

Mark stood up and leaned over the table, extending a hand for me to shake.

"Hello Karen. I'm Mark, this is Steven, Sue and Ben." Each of them shake my hand in turn, and I make sure I grip back firmly, and look them in the eye as we exchange pleasantries. To my surprise, the older woman Sue, has the toughest hand shake.

"Please, take a seat."

Mark comes around to my side of the desk and pulls over an armchair for me to sit in. This seems strange at first, as the others are all sitting on normal desk-style chairs. But then I remember, feeling stupid, that the scene I've had to prepare involve me sitting down in an armchair. I'm suddenly thankful I kept my mouth shut.

"Well." Says Mark, taking the lead, "We've been very keen to meet with you Karen." Out of the corner of my eye, I see Cumberbatch nod, as he looks down at the papers in his hand. I wonder what he is looking at, until I remember that his Sherlock Holmes character is in the scene I'm about to read. Of course he is. Holmes and Watson are a double act. Everyone knows that.

"I'm thankful for the opportunity Mr Gatiss."

"Oh, please! Call me Mark. And you're welcome. Shall we start with the scene? Ben? Sue? Would you read Mrs Hudson?"

He speaks. "Of course." Then he and Sue stand up and bring their chairs over by mine.

I turn my brain over to the scene, watching as Steven silently reaches over and turns on a camera mounted on a tripod, pointing right at me.

"Ah! Yes! A case! Finally! Mrs Hudson? I'll be late back. I'll need something to eat."

I am momentarily startled as Cumberbatch's deep voice suddenly fills the room, cold and snappy. Holmes.

"I'm your landlady, dear. Not your housekeeper." Sue pipes up as Mrs Hudson.

"Something cold will do. Joanna? You stay here, put your feet up. Have a cup of tea."

With that, Cumberbatch stood up and hurried out of shot, leaving Sue and I alone together.

"It's alright dear, I'll get you a cup of tea. You sit there and rest your leg."

Here we go…

"Damn my leg! Sorry, I'm so sorry. Yes, a cup of tea would be lovely thank you."

Cumberbatch came back into shot and looked down at me with a quizzical smirk.

"You're an army doctor."

"That's right."

"Seen some nasty things I bet. Bloody deaths and the like."

"Oh yes. Too much. Far too much."

"Would you like to see some more?"

"Oh god, yes."

With that, I stood, and following Cumberbatch, limped out of shot. No one had told me to put on a limp, but without it, the "damn my leg" line made no sense…

"Cut!" That was Mark.

"Thank you Karen! That was lovely! Please, sit back down and we'll talk."

Talk? This was rather new. Normally after doing a scene it was all "thank you so much for coming in. We'll call you." Sitting down to talk was very different.

"So…" Mark began, "I personally loved your angry delivery of "damn my leg!" Tell me why you feel she'd snap at poor Mrs Hudson like that?"

This feels like a very strange job interview…