He picked up a small sample of black plastic mesh and pulled at it. ‘This is fish netting. I think it is too easily distorted to be the one you are looking for. At the other end of the scale is this.’ He showed her a grey translucent mesh, with four large circular holes. ‘You know what this is?’

‘I’m from Glasgow, of course I do.’ She laughed. ‘It’s the webbing from a pack of beer cans.’

‘That’s right. Now, the webbing is polypropylene and the other is polyethylene. This one, I think, is too rigid to be the mesh that you are looking for. I do wish you had a sample of it that I could test, then we could get to the root of the problem immediately. Think I’m going to need a lot more time.’

‘I’m not surprised,’ Rainy said. ‘It’s like starting with the suntan on a corpse and trying to work back to find the bikini she was wearing.’

The academic’s eyebrows almost shot off the top of his head.

‘I was actually thinking of hysteresis,’ he said. ‘The extent to which a stretched or deformed material will return to its previous shape.’

Saturday morning arrived gently, for once without the insistent ringing of the alarm clock. The first thing Gillard was aware of was the warm proximity of Sam, her dark hair resting on his chest, the red varnished nails of her fingers hooked on one shoulder. In theory Gillard had the day off, a rare treat during such a busy case. Claire Mulholland had volunteered for the weekend shift, to allow the detective chief inspector to spend a little time with his recuperating wife and visit his Aunt Trish, who was still in a coma in hospital. She had promised to ring if anything dramatic occurred, but Gillard knew she would take care of all but the biggest developments.

He kissed Sam gently on the cheek, slipped out from her arm and checked his phone. Good. Nothing important was notified. He slipped on a bathrobe and made his way downstairs to put the kettle on. Last night Sam had announced that if the weather was good they were going to go for a picnic at Box Hill, a famous beauty spot on the North Downs, a half-hour’s drive away. Peering through the window, he saw a cloudless sky. He opened the fridge and found Sam had already cooked tandoori chicken drumsticks, along with home-made spicy samosas. There was chicken and ham pie from the local deli, and a home-made red cabbage coleslaw.