He’s been eyeing me up for a while, and suddenly sees his chance. I’m in the waiting area for Nellie’s clinic at the AMC and a trolley with soiled bedding moves between us, but the second it’s past he slips off his seat, one foot finding the floor tentatively, then the other. He moves quickly across the space, all the while his eyes staring at mine. He reaches me and I can hear his breathing, heavy and laboured. He has something in his hand and he raises it slowly and then stabs my leg over and over again. A grin cracks his face open and a long line of drool spills out of his mouth. Snot-crusts round each nostril.

‘Darling, darling, don’t do that,’ says a woman’s voice in English.

She hustles over and tries to stop any more crayon damage, though this kid’s got the kind of persistence that makes global CEOs. Or serial killers. And maybe it’s just my mood, but I don’t like the look in his eyes. It seems cold somehow, like there’s a dark intelligence in there, watching, waiting. The woman gives me a weak smile and an even weaker apology, which somehow seems to convey the message that it was actually all my fault anyway.

Perched on her hip is another child, who, from the way she’s cradling her, is the reason they’re here. She looks like a nice kid, a little shy maybe, and I feel bad for her, the situation she’s in, even though I know Nellie’s going to be able to help her quality of life no end. The woman eventually manages to drag her son across the waiting area and gets him to sit back on his chair, where he sits and stares at me, a colouring book open but untouched in his lap. He’s still holding the crayon aloft in an overhand grip. I look at the marks on my jeans and decide the crayon-slasher could do with some psychological screening for the good of society.

Suddenly the young girl makes a strange strangled gurgle. I watch as she shakes, before all her muscles go rigid. Her mother holds her, rocking slightly. Saliva bubbles into a foam at the girl’s mouth.

After a few moments, the seizure lessens and her muscles become less rigid. I’m no doctor, but I’ve been round Nellie long enough to know that she has Dravet syndrome, a severe form of epilepsy which occurs very early on in a child’s life. And one for which, up until now, there was no cure.

‘The doctor will see you now.’