Written for prompt 7 (penna a sfera/ballpoint pen) of maritombola; it's like the Italian version of bingo, only better.
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"I assure you, madam," the Doctor says. "We are professionals."
The short-sighted alien at the desk peers at them, frowning as he (or possibly she) takes in the Doctor's eccentric apparel, his bow-tie and his hopeful grin. He frowns even more as he moves his stare to Amy.
"Wait a moment while I check," the alien says, turning away from them and picking up some sort of telephone receiver.
Amy nudges the Doctor in the ribs. "Couldn't you just show him the magic piece of paper?" she hisses.
"Nah," the Doctor replies. "High-security place like this, all of their employees must have some kind of psychic training. Well," he adds after the briefest hesitation, "unless we're very, very lucky. But I'd rather use that luck to convince this lady that we're professionals. Try to look professional, Pond."
"Wait, high-security?" Amy asks. She straightens up as best as she can and tries to act as if she knows exactly why they're here, though to be honest she doesn't have the foggiest. "I thought we were just here to see a friend of yours."
"Yes, long story, he might not want to see me," the Doctor replies.
"Why, did you do something to him?"
"Not yet, at least for the next five years," the Doctor says.
Amy is torn between wanting to ask him more and not wanting to hear an explanation that's very likely to give her a headache.
She's saved when the alien at the desk turns back and says, "Mr. Smith, Ms. Pond, I will need to check your toolkit before letting you downstairs."
"Of course!" the Doctor exclaims, producing the sonic screwdriver from his pocket and handing it over.
The alien turns it over in his (no, her!) hands for a couple of seconds before handing it back. "All seems fine. Ms. Pond?"
"Oh, I'm not carrying one of those," Amy says, prompting the alien to snort and the Doctor to wave his hands around frantically.
"Don't be silly, Pond, of course you do," he says. "What kind of professional you'd be if you forgot your toolkit?"
He's wiggling his eyebrows, possibly trying to send her some kind of message, but Amy has no idea of what he wants her to do. Couldn't he have told her earlier about this part of the plan?
At a loss, she puts her hands in her jacket's pockets and finds a ballpoint pen. "Er," she said, holding it up hesitantly.
The alien rolls her eyes and snatches it from her hand, only giving it a cursory glance before tossing it back. "You can go," she says, pressing a button to unlock the elevator's door. "Try not to take too long, we're expecting visitors soon."
Before the Doctor can talk her, she's already started another phone call.
Amy grins. "I can't believe that worked," she says as they walk away from the desk.
"Neither do I," the Doctor replies. "By the way: a ballpoint pen? Seriously?"
"Hey, it's not as if humans go around carrying alien screwdrivers," Amy replies defensively. "And it's my favourite pen. It writes in green," she adds.
"Ah, well, in that case," the Doctor says. "Hurry up before they realize that we're not really here for maintenance."