"I'm going to ask you a question," says the American woman, still on the threshold. Taking off her coat as if she expects to stay. Hope she's boring. New England, new money – someone else's money, keeps two African Grey parrots in a cage too small for them; the sort of person I'd love to send away. But then she continues, "If you say yes, I'll live." Which implies something about if I say No and everything gets a little bit interesting. "Choose not to help me and it's on your conscience."

Alright. Perhaps I won't throw her out right away.

I watch her as she makes her way to the client's chair. There's a science, a precision, in the way her eyes take in the room. The violin, the sword among the umbrellas, the clocks and sculptures. Anything with a lock on it. "Intriguing," I murmur.

"Yeah, I thought that would get your attention."

"No, your opening gambit, while amusing, did little more than get you in off the stairs. What's intriguing is that it's not usually the thief themselves who approaches me."

"Huh? Oh, no. Not me, anymore. I've changed my profession. But the old habits die hard. We met, actually, when I was in my old job. I was on the far end of a satellite transmission, but you still caught me."

"…Lambeth Emeralds." A diverting case, though that might just have been the effect of having the Atlantic Ocean in between myself and the crime scene. This woman in front of me wandered straight into the office of a sprawling manor home, setting off the alarms. She then hid in the scotch cupboard beneath the desk while the owner searched the room, allowing her to watch the safe being opened. When he left the room she had approximately forty seconds to take the emeralds and hide herself again. "Didn't you go to prison?"

"No evidence. Not the sort that juries go for."

You'd think the truth would be enough. Tell people the only possible story and they'll ask you where the fingerprints are, and the fibre evidence.

"So you got off. Well done. And I assume the emeralds put you in good stead."

"And I went legit," she says, with wide-eyed girl-scout honesty. Or, in other words, with no honesty at all. She even has her right hand up in prayer. That lasts about a second before one finger elongates and taps the air, "Almost."

It's as close to the truth as she knows how to tell. The real story is more complicated. There is a mark on her belt where she had to let it out a notch or two; she tried legitimacy. She ate, drank, was merry, had an ill-advised affair. Boredom began to seep in. Slowly at first, and then an overwhelming sea-change, murderous, crushing. Legitimacy almost killed her. The money running out was probably the best thing that could have happened to her. The only thing I cannot quite divine is what business precisely she has found herself in now.

But surely there's something more dignified than just asking… "What has any of this got to do with the proposition that got you into this room?"

"Lately I've moved into… Maybe you'd call it counselling? I help the bereaved to resolve their issues with the deceased and move on with their lives."

Oh, dear God. It doesn't take much reading between the lines to know what sort of scum I've currently got in the flat with me. I get up and move past her, headed for the door, which I fully intend to hold open until she is gone. Even then, I'll be working from the kitchen until the smell of her perfume disappears. It's expensive and classic and if this is how she earns her money she doesn't deserve the bloody stench.

But she spots what I'm doing, "No-no-no, c'mon. You don't want to be an accomplice to my murder. Which you are, technically, if I tell you it's going to happen and you do nothing. Accessory before the fact."

"The law has some very interesting things to say about fake psychics too, Miss…?"

"I told you, we've met before."

"I'm not in the habit of retaining the names of criminals who were lucky to be worthy of my attention even once."

She bristles. Vanity, pride, conceit, arrogance; now that I think about it, she might have found her calling in the con game. Maybe theft was never for her. "Carvelle. Laura Carvelle."

"Charmed. Now kindly leave." I throw open the door and stand with my hand on the edge. Her heretofore perfect posture sinks, face gone blank as the world collapses in on her – "There. Now you look like a woman in fear of her life." It's surprising how quickly she resets. The anger helps, I think. Her self-possession returns, but her teeth are set on edge now, eyes narrow. "You're a professional liar. I had to check."

By the time I've shut the door again and come back to my seat, Ms Carvelle has straightened her back again. "Medium," she says.

"I don't understand."

"You said fake psychic. Psychic looks into the future. It's a medium that contacts the dead. I'm a fake medium." At this particular moment she doesn't look especially mystical or especially haunted. Then again, her coming to me is another sort of business altogether. I imagine when it comes to her idiot punters she can turn it on rather well; her perfume is not the only sign of prosperity. Her shoes, for instance, may well have been taken fresh from the box just this morning. There's a bulge in her pocket the precise shape and weight of a mobile phone released to the public only last week.

"Then I suppose I ought to explain that, whatever you expect to get from me, you're unlikely to get it, rather than expecting you to read my mind."

"That would be a fake telepath." It doesn't take much of a glare to wilt her. "Okay, okay. A woman came to me lately. She'd lost a young daughter. Which is a tragedy, and she was in pieces. Lucky for me it was a pretty high profile case so the research was easy. And I helped her to put some of those pieces back together."

"What do you mean, 'high profile'?"

"Little girl's name was Macy Diver."

Ah. A much publicised case. Macy Diver underwent routine surgery to correct an eye complaint. It went well and she was sent to recovery for the anaesthetic to wear off. She never woke up. Four years old. "I assume you agreed to see Mrs Diver without knowing who Mr Diver was."

"Get out."

"Oh, c'mon, let me finish!"

"Leave, now. I'm not in the habit of showing sympathy to those who have knowingly flung themselves into the firing line. It's tantamount to suicide."

Panicking now, sitting forward out of the chair, "But… accessory. Didn't I just explain about you being-?"

"Only if I believe you. If I have reason not to believe, or to believe I'm endangering myself, both of which are plausible arguments, then I'm off the hook. Therefore, though with my very best wishes, take your fetid presence far from me."

Miss Carvelle reaches into her pocket. Calmly, and with the grace at least to look mildly ashamed of herself, she shows me the screen and the ongoing recording of this conversation. Before I can say or do anything else, she ends it and, so far as I can tell, sends it to someone. "That's gone to my lawyer. He knows I came here and now he has that. If anything happens to me he's under instructions to go through the police first, and the press if that doesn't have the desired effect."

Damn. A filthy play. But what more could I have expected? She thinks it's a pretty sort of a play. In fairness, it probably is the smartest thing she's done in a while. There are still ways around it, I suppose, but… "Alright, keep talking."

"Okay, so like I said, I was helping Mrs Diver get somewhere. She's a lovely person. And whatever helps, right? If she wants to know her little girl made it safely to the big cloudy playground, you name me one person alive that would tell her no." I will admit, grudgingly, to a certain fascination with the lies that the lowest of the low will tell themselves in order to sleep at night. That is the only reason I allow this to pass unchallenged. "But Mr Diver, turns out, wasn't crazy about her paying for the service. And Mr Diver-"

"-Is a violent lunatic who has the patellas of his business associates shattered for getting into five pounds debt."

"That's a myth. He says it was fifteen pounds. So now he wants to sit in on our session tomorrow night. Long story short, I need to perform. I need to know something nobody knows but them, and me not being a psychic or a telepath or-"

"-or a medium."

"Yes, thank you, or a medium…"

I take a moment to make all the facts sit neatly. If I intend to condemn her, and for the most part I do, I ought to at least make sure I understand. In order to be suitably impressive and avoid being shot in the back of the head, Miss Carvelle here would like me to assist. She wants me to look at the Divers and deduce something about their recent brutal heartbreak.

As I am thinking all of this, as if in answer, "Well, isn't that what you do? I mean, you look at people and you know things they've never told anyone. You're the only one who can help me."

I can promise you now, neither you nor Laura Carvelle understands the reasons when I say, "Alright." You don't know half as much as you think you do.