‘You say you didn’t get even a glimpse of his face?’ Gillard asked her.

‘No. I was too busy unlocking the phone. I honestly only saw him in peripheral vision.’

‘So how do you know it was a him and not a her?’ Quoroshi asked.

Mockett paused. ‘I can’t say, but there was something about the movement, I don’t know what it was. I’m sure it was a man. It’s the way when you see someone moving in the far distance, too far away to make out their features, you still know somehow whether they are male or female.’

Gillard nodded. ‘Based on your pictures, the assailant cycled up behind the woman, and hit her with something. He then dismounted, allowing the bike to fall sideways into the snow, where the tip of the right pedal and the tip of the right brake lever left an impression. While he was off the bike, and she was presumably already on the ground, he continued to strike her a number of times.’

‘It certainly was a savage and furious assault,’ Quoroshi said. ‘Far more blows I would have thought than were required to kill this lady.’

‘So, Yaz, what can we do about this to make it suitable to offer in evidence? You could hardly offer a patch of snow for a jury to inspect.’

‘I’m going to try to make a cast. I was thinking about this earlier, and found a section on the Alaska police website where they talk about having to create a permanent impression of footprints or tyre tracks in snow. I’m not sure we have the materials they mention easily to hand but I’m going to take a look.’

Fine specks of snow like polystyrene pellets peppered the windscreen of Gillard’s unmarked grey Vauxhall as he drove DC Gabby Underwood up the M3 motorway towards the prosperous south-west London suburb of Richmond upon Thames. Mrs Roy’s residence was a four-storey Georgian house, on a quiet side road just a stone’s throw from the river. It was protected from view by a large laurel hedge and a pair of wrought iron gates. The detective nosed the car up to the gates, and identified himself at the video box on the gate post. The gate slid silently open. He parked carefully between a new Mercedes and a Jaguar convertible whose wing mirrors alone were probably worth more than the Vauxhall. He and Gabby made their way to the pillared portico, but before they had a chance to ring the ornate brass bell, the door opened. A striking-looking thirtyish Asian woman with cropped snow-white hair beckoned them inside. She was swathed in a pea-green woollen dress, off her shoulder on one side, and with sleeves so long they swallowed her hands. Her bare coffee-coloured feet were decorated with a fine tracery of henna.

Gillard introduced himself and Gabby, and offered his condolences.

The woman nodded. ‘I’m Kiara, the baby of the family,’ she said, lifting a sleeve and offering them the most perfunctory of handshakes. Expecting flesh, Gillard glanced down. The woman was wearing fine silk gloves that perfectly matched her skin tone. ‘Rotten freezing weather again. Would you like some tea?’ They replied in the affirmative, and she shouted something down the hallway behind her, ending with the word chai. The entrance hall was sumptuously decorated in gold and green, with a black and white tiled floor. It was dominated by a man-sized porcelain statue of the elephant-headed god Ganesh, and a large gilt mirror behind. The chandelier above them was an elaborate modern creation with a dozen arms at different heights suspending thousands of glass teardrops.