A small suburban park, her usual exercise destination, was only a half mile away, but today she was going to go to the common. It was twice as far away but the combination of woods, rolling hills and open grassland was a far better setting to revel in this wintry weather. She ran up Woodfield Lane, past Ashtead Station to her left, over the level crossing and, where the road swung right past a bungalow, she continued straight on. This was a paved bridleway onto the common. She stopped at the vehicle barrier, breathing heavily, but feeling warmth already seeping into fingers and toes. With no one about, she was able to use the top of the metal gate for her hamstring stretches and warm up routine without self-consciousness. Of the three vehicles parked near the start of the track, one had clearly been there overnight, based on its complete covering of snow. The second, a lightly dusted olive­green Jeep Cherokee, had been parked a few minutes ago, because the flakes landing on its bonnet melted immediately. Only now did she notice the third – a dirty white Toyota estate, windscreen wipers moving, the male driver’s face discernible as shadow within. Two minutes later, at 7.18 a.m., she set off along the snowy path at a gentle pace. With slippery ground this was not a day for breaking records, but merely for enjoying the beauty. Five minutes into her run, Kirsty passed a middle-aged Asian woman, striding along the edge of a brake of coppiced hazel woodland. The woman was using a ball thrower to exercise her energetic boxer dog. The muscular animal, racing for a tennis ball thrown far to her left, tore in front of Kirsty, causing her to check her stride.

‘Oh Bertie, don’t be so rude,’ the woman shouted. Kirsty threw back a smile at the woman. Shortly after, she turned off right to do a woodland loop, and upped the pace. She was only three minutes into her jog, luxuriating in the silent whiteness of the world, and the carpet of untrodden snow ahead.

Her relaxation was torn asunder by a piercing, bloodcurdling shriek followed by the frenzied barking of a dog. She paused for only a second, sweat transmuting into ice. Something terrible had just happened and she knew what she had to do. Pivoting towards the sound of the animal, she exploded into a sprint. There were no more screams, but the first still echoed in her head.

She burst out of the woods and turned left onto the main path, racing towards the noise. She pulled out her mobile from the sleeve pocket. Too busy unlocking the screen, she almost collided with a hooded mountain biker, a whirl of dark colours going full tilt in the opposite direction. The boxer was 200 yards ahead, racing in circles, barking angrily. It rushed towards the edge of the trees and halted, whimpering, before resuming its circuit. As Kirsty approached she could now see the woman was lying on the ground. The dog rounded on her, blocking her approach, snarling. It had blood on its face and head.