The Hampshire Constabulary Range Rover arrived within ten minutes. PC Colin Andrews emerged from the vehicle into the pouring rain, while colleagues from other patrol cars closed off the carriageway. He donned wellingtons and latex gloves and picked up a powerful torch. The beam followed the trail of damage, which included a broken stanchion on a large green road sign, into the undergrowth. No tyre marks on the carriageway, perhaps not surprising in the weather. Still, the exit route was straight, which indicated the vehicle had remained under control. No evidence of last-minute braking.

Very strange. Almost as if this was intentional.

He set off to follow the path of smashed stems and flattened nettles, heading up and over the embankment then down towards the river. He radioed in his findings, then followed the trail of destruction, steadying himself with a hand on some saplings as he began the muddy descent. There, fifty yards further down in the beam of his torch, was the Volvo, on its roof, in the shallows. The tail lights were still on. With only one hand to guide him, the other holding the light, the steep descent through the wrecked bushes and churned earth was treacherous. Finally, he stumbled through the broken branches of a weeping willow and plunged up to his knees in water. The car lay ten yards from the edge of the bank, held above the full depth by the felled boughs of trees. Wading across, his wellies now full of water, he shone his beam in through the crazed windscreen and between the inflated airbags. There was no one visible.

‘Call out if you can,’ he shouted, over the sibilant waters, hissing over the stones. There was no reply. The driver-side door was creased inwards, the window frosted and broken, shards of glass curled outwards. He squatted down in the shallows and shone the torch horizontally. There appeared to be no one in the car. At the limits of what he could do without wading waist-deep into the river, he was relieved to hear the sound of approaching sirens. Back up on the bridge he saw fire appliances, an ambulance and a recovery vehicle, and made his way back to brief them.

‘Any casualties?’ asked the burly fire chief who greeted him.

‘Not that I can see,’ Andrews replied. ‘Wriggled out somehow through the driver-side window. Miraculous, really. Probably a drugged-up joyrider. Who else goes the wrong way up a dual carriageway?’

The next day

DI Helen Kaplan of Hampshire Constabulary rang the doorbell at 14 Wycherley Crescent, Hemel Hempstead. The woman who came to the door was a trim fifty-something with silvery hair. Kaplan introduced herself to Angela Blanchard.

‘Any news on the search?’ Angela asked, showing the detective into the lounge. A long-haired cat was lying splayed out in the middle of a white leatherette settee, leaving the women to sit on the other two components of the three-piece suite.