His older brother, he tells me. Three weeks ago. Car accident.

     I disappear into the back room and return with a modest jar. I've learned to start small. We usually get only drops at this stage.

     Maybe this is a mistake, he says.

     You're here now, I say, placing the sealed jar in the centre of the round table between us. We may as well talk. His eyes tumble down my face and settle on the jar. It's free, I remind him.

     He doesn't leave — they never do — and so we begin. He talks, and I listen. I imagine that I'm unravelling a knot of knots, teasing his fibres apart, probing for the core of his grief. They loosen with ease under my experienced fingertips, only to stretch into a single taut, thick rope as his defences rise. At this early point, where the loss is still raw, the effort is huge. I pull with all my might as if I'm hauling up a heavy bucket from some great depth. Eventually, it snaps. When I open my eyes, his face is less grey, his head better squared between his shoulders. Between us, the jar is no longer empty. I pick it up and examine the grief we have extracted: a pale, cloudy liquid. Only a few spoonfuls, but it's a start.

     When I show him out, there are already two others in the waiting room. One is a regular. She's been grieving for so long that it's become a part of her, and while it's normal for each subsequent session to become easier, hers have begun to trend the opposite. She's afraid there will be nothing of her left by the end. And yet, she still comes. My battle with her grief has become another part of her. I hate to say it, but I fear we are becoming of little use to one another.

     After the first few hours, I take a break. The jars are piling up, and I must do something before they become immovable. I wake my laptop and log on to the marketplace. It's only here that my art becomes transactional, as eventually, it must. My website is invite-only, and it's taken me years on niche and sometimes questionable forums to cultivate a loyal customer base. That may sound sinister, but it's the price of preserving my clients' privacy. It's not perfect, but I can't very well keep the filled jars to myself – I'm running low on shelf space as it is. And what I have is a very special skill – why should I not monetise it?

     I add each jar as a listing, with a photograph and some basic information. After publishing, my anonymous collectors will gather. After the auction closes, I'll pack up each jar and ship it off to the winner at some nondescript PO box. I'm careful never to find out what they do with it.

     In the park outside, the seagulls have quietened, and the market is alive with bustle. Halfway down, a dark figure sits on one of the benches – the one with the inscription For Rachel, who fed the birds. In contrast to the bright sunshine, the man is a hole in the world. He rises the moment I flip the sign on the door back to 'OPEN.' Something in my belly tightens as he approaches.

     Who has he lost?

     I don't know his name, he says. His voice is low. His eyes are shiny, dark beetles. I tense up.

     How long ago?

     Last night.

     I watch him. He's a spider above my bed, watching me back. I don't ask the final question: How?

     He intertwines his fingers in his lap. I can see dark flecks under his nails. I wonder if he's an artist.

     I go to the back room. I could slip out the back door to where the bins sit, foul and fox-raided, and phone the police. But I don't.

     I return with a medium-sized jar, a tall, narrow one with a cork in the top. I've had to guess which I dislike more than anything. I place it between us.

     Tell me, I say.

     This time there's no knot to unravel, no rope on which to pull. When I close my eyes, his grief is everywhere, black and furious, and I struggle to find purchase. The things he tells me are repugnant, so I force the blood to rise between my ears to drown him out. His grief burns to the touch like I've plunged my hands into a vast belt sander up to the elbows, my brittle bones and ragged nerves quickly filed to dust. His voice persists through the pain, a squalid drone of violence. I grasp at great clods of his searing agony and pull.

     By the time I recover, spots bursting in my eyes, he's gone. The tall jar has filled up with an inscrutable black liquid that has pushed out the cork and spilled onto the table. When the dizziness subsides, I close the office and lower the blinds. I try to wipe the bubbling tar from the table, but it leaves sticky residue in the grain and drops thickly onto the floor. I clean the jar as best I can and take a picture. On my laptop, I add it to the online shop, my trembling hands making mistakes as I type. I give it a lot number. In its description, I write simply, 'Murderer.'

     I publish, and within seconds there is a clamouring. The numbers rise. I begin to receive urgent messages from customers.

     I must have it, one collector writes. I will pay any price.

     I check the current bid. It's far higher than I've had before. It continues to rise.

     Will there be more? asks another.

     I peer through the blinds and see him drifting through the market stalls. He looks like he could melt away in the wind. He stops to chat with one of the sellers, hands idly pushed into his pockets. For the briefest instant, he looks back at me between the blinds.

     Yes, I reply.