‘She’s not done her roots recently,’ noted Gillard.

‘Yes, but look below that half inch of white. There is a thin layer of dark pigmentation, very close to the root. I remembered reading something about this from when I was a student, and had to look it up to be sure. I tested the hair in hydrogen peroxide, which confirms my initial suspicion, although I still hope I turn out to be wrong. Look at her toenails.’

Gillard looked at the nails, which looked misshapen. ‘Bit twisted,’ he said.

‘It’s not so much that as this, which is known as a Mees’ line.’ Delahaye pointed to a thin white line a third of the way up her big toenail. ‘The nails and hair are effectively a tape recorder for some types of toxic exposure, and because of their natural rate of growth they give us some idea of the time it happened.’

‘What do you suspect?’

‘I think she may have been exposed to thallium, which is a potent and gradual poison and also causes alopecia. I’ve taken samples from the kidneys, which excrete the toxic chemical, and of course we would also find it in her urine and faeces.’

‘Ah. She drank her own urine, apparently.’

‘Really? Hmm. It’s not unheard of as a folk remedy in the subcontinent. That certainly wouldn’t help matters, as she would reabsorb what the kidneys had just flushed out.’

‘Could this exposure be accidental?’

‘Fifty or a hundred years ago, I would say yes. The most common exposure is in rudimentary rodenticides. In Britain in the present day, it would be pretty difficult to stumble across thallium by accident. If she was, let us say, active in metal processing, working with cadmium, lead or zinc, there would be a possibility of occupational contamination. As the victim is of Indian ethnicity, it might be a visit home that could have provided the exposure.’

Gillard pursed his lips. ‘Her passport shows no visit to India in the last six months. Indeed she’s not been out of Europe in that time. It sounds like you’re dubious that it could be an accident?’

‘I really don’t want to rush to judgement until I have her medical records and received the toxicology results. That should be this week. If the victim had reported any neurological symptoms to her doctor in recent weeks and months, that would certainly be a confirming outcome. It would tend to show itself as peripheral neuropathy, feelings of numbness in fingertips and toes, and some gastrointestinal symptoms, principally constipation.’

‘The family did say she’d been feeling tired and stressed.’

Delahaye chuckled and adjusted his glasses. ‘Well, that puts her in the same boat as more than half the population. I think we’ll need something a bit more specific.’

The mug smashed against the wall, splattering dregs of coffee all over the expensive flock wallpaper that had only been hung by an interior designer six months ago.

‘You idiot,’ Prisha said to Simon, who cringed on the sofa where he was lying full-length, iced daiquiri in hand. ‘I thought you’d stopped.’