Jack headed up the winding, double staircase, pausing to look at the family portraits lining the panelled walls. Mathew was in most pictures, but his face was always turned away from the camera and he rarely smiled. Not that he looked sad; it was just as though he was in a perpetual state of deep thought. One photo, taking pride of place on the landing where the staircases met, was of Sally, George and Mathew, aged about eight, running around the garden playing what looked like a game of tag, and it stood out from the rest. The glee on Mathew’s face was so animated and unrestrained that Jack couldn’t take his eyes off the image. It was slightly blurred and the composition was awful, but this photograph was clearly positioned there to be the first one this family saw in the morning and the last one they saw at night.

Jack felt his heart quicken with parental understanding, and once again he thanked his lucky stars that his daughter was, as far as he knew, a healthy little girl who was on track to live a normal, happy life.

‘Took two hours to get that, apparently.’ Jack turned to see Nathaniel standing outside Mathew’s bedroom. ‘It took Matty a while to get the hang of why he’d want to run away from his parents but, once he twigged that dodging a touch from your mum or dad was actually fun, there was no stopping him. Matty’s in a good mood and is looking forward to your chat. Give him his space though, and please don’t touch any of his things.’

Mathew’s bedroom was bright and light. It was really just a white box; a blank canvas on which he could display his obsession with Game of Thrones, with myriad posters, character figurines and other merchandise, as well as DVDs, well-thumbed books and T-shirts. Mathew sat at his desk, playing Game of Thrones Ascent which was being displayed simultaneously on two large Mac screens and was hooked up to surround sound, though at the moment the sound was nothing more than a dull buzzing coming from the headphones which were hooked over the back of Mathew’s chair.

Mathew paused his game and spun his wide, heavy leather gaming chair, so that he was side-on to Jack. ‘Well, well, well.’ Mathew’s deep, resonating voice was a surprising contrast to the high-pitched screaming Jack had heard on the police bodycam footage. ‘It’s the diminutive Detective Sergeant Warr.’