They jogged easily along the path towards the nature reserve, moving through mixed woodland where in many places the snow had not yet melted. The tracks were easy to follow, and there were several muddy patches where Gillard knelt down to take photographs, placing a coin beside the impression to give a sense of scale. The type of tyre thus recorded, they upped their pace, finding no other bike tracks since the snowfall to confuse the route. It was not yet eight, and Gillard hoped that on a Sunday morning luck might well be on their side.

Finally they emerged by a public footpath sign onto a main road, the A243, close to Leatherhead Golf Club. It was here that the tyre tracks disappeared. There were no parking places or pull-ins designated nearby and no evidence of vehicles parked on the snowy verge. Gillard flagged down a passing patrol car, and got them both a lift back.

Half an hour later, Kirsty was sitting in an interview room in Epsom police station, having given her statement, and now watching DCI Gillard consume an enormous bacon sandwich. ‘Are you sure you don’t want one?’ he asked, as he wiped ketchup from the corner of his mouth with a napkin.

‘I’m a vegan,’ Kirsty said.

‘Then I suppose I’m committing an unforgivable crime against the animal kingdom,’ he said.

‘Look, I’m not a crusader. But you’re not doing yourself any good.’

He nodded and raised his eyebrows, and tossed the napkin into a bin, signalling the end of the conversation.

‘So what happens to Bertie the boxer?’ Kirsty asked.

‘Given that we have a dead body on the slab, I’m interested that’s the first question that you asked. But he’ll be looked after by the local dog handling section.’

‘Have they done a DNA check around his mouth?’

Gillard looked up quizzically.

‘I definitely saw bloodstains around his mouth, as if he had bitten the assailant.’

‘I’ll ask them to do it, but I’m a little dubious that we will get anything. Any human DNA traces may well have been overwhelmed by doggy saliva. On the other hand, we can look out for fragments of clothing, which may contain the cyclist’s DNA.’

‘Do you know who the victim is?’

‘Yes, she’s Mrs Tanvi Roy, quite a notable businesswoman apparently,’ Gillard said. ‘Yaz Quoroshi of CSI say there’s plenty of ID on the body, though no purse. I shall be going round to see her next of kin this evening, though it seems they’ve already picked up the bad news, according to my family liaison officer.’

Kirsty nodded.

‘When is it you are due to start as a CSI?’

‘Tomorrow. Based in Mount Browne to begin with, reporting to Mr Quoroshi.’

Gillard smiled at her. ‘Well, this morning has been quite an induction for you, hasn’t it?’

‘To put it mildly.’

‘I think you should be very pleased with yourself. And I think we should both go over this afternoon and have a look at this snow sample that you collected.’