Gillard looked dubiously at the jar before bringing out a plastic evidence bag from his jacket pocket and sealing the jar inside.

Kiara shook her head. ‘So you’re really taking the piss?’

‘Yes. Would you like a receipt?’

Gillard’s next stop was Mrs Roy’s flat in Leatherhead. A CSI van was already outside, and he saw two male officers in Tyvek suits, booties, gloves and hairnets carrying out cardboard boxes stacked with foodstuffs. He stepped into the kitchen and found CSI chief, Yaz Quoroshi, looking at a tray of health supplements.

‘Hi Yaz,’ Gillard said. ‘They don’t need to be suited up for this, do they?’

‘No. These are the new trainees, I thought I’d get them involved in something harmless to get them used to moving about wearing all the clobber.’

The crackling of plastic heralded the arrival of a young woman from the bathroom. Despite the hairnet and paper dust mask, Gillard recognised Kirsty Mockett. She was carrying a cardboard box full of toiletries, and smiled with her eyes as she squeezed past on her way to the van. Once she was out of earshot, Gillard asked: ‘How is she doing?’

Yaz glanced sideways towards the van. ‘Fine. Eager to learn, not too full of her own self-importance. I think she’ll do well.’ Turning back to the health supplements, he said: ‘I understand everything is to be checked for contaminants.’

‘That’s right,’ Gillard said. ‘Delahaye believes she may have ingested thallium.’

The CSI head eyed him warily. ‘Mass spectrometry is the way they test for that, I think. It’s going to be expensive for all that lot. I’m a bit surprised at this, seeing as you have already charged someone. Or am I missing something here?’

Gillard tried his best at a confident smile, though he felt anything but. ‘It’s just another line of inquiry. The toxicology results were ambiguous and we just want to see if there’s an accidental or criminal cause for it. We wouldn’t want to overlook anything that turns out to be significant.’

Quoroshi nodded. ‘DCI Gillard, always careful, always cautious.’ He clapped him affectionately on the shoulder. It made him feel like a complete fraud.

He made his way around to the back of the van, where the CSI trainees were stripping off their plastic suits.

‘I’m glad to get out of that,’ said one of the male officers, whom Gillard remembered was called Ryan something. He had a thin film of sweat across the forehead, and his eyes slid sideways to Kirsty, who was wriggling rather sensuously out of her suit. The DCI couldn’t entirely blame him – the woman had a great figure, now emerging from the plastic like a butterfly from a cocoon.

‘Got some more stuff for you,’ Gillard said, handing across to Ryan a bag of recyclable containers he’d recovered from a wheelie bin.

‘So, what are you going to do with all that?’ Kirsty asked.

‘We going to get it tested for a poison called thallium.’

‘I thought she got whacked over the head,’ Ryan said, sharing a glance with his mate.