Think, Fleet urged himself. He had to presume Isaac had been waiting to pounce on Richardson the moment the panic in the chapel set in. So what then? Would he have dealt with Richardson at the first opportunity, left his body to be consumed by the flames? But if so, why set two fires? If it was just to ensure the school burned down as well, why not start the blaze more centrally, rather than in the wing of the building where the fire would be slowest to spread?

As if in answer, the bell in the clock tower at the front of the school began its hourly toll, the chimes resonating above the noise of the flames like a fire warning in a medieval village. Between the gongs there was a wail of approaching sirens. The fire engines had got past those news crews, then, as well as the cars clogging the drive. Now they just needed to negotiate the crowd at the front of the building.

The crowd … the news crews …

Fleet’s gaze snapped to the stream of people being herded by his colleagues towards the car park. He thought of Isaac gazing up into the CCTV camera in Richardson’s living room, his look an obvious challenge. Your turn to hide, his note had read – suggesting he didn’t just want to punish Richardson. He wanted to scare him. To humiliate him. And all at once Fleet thought he knew how.

He turned, grabbing Bevan by the sleeve. The DC still had his phone to his ear.

‘Talk as we go!’ Fleet instructed.

‘But … what about him?’ Bevan signalled with his chin towards the headmaster.

Harris was rooted to the spot, his robes hanging off him like a broken sail, the fire flickering weakly in his tear-filled eyes. It was obvious he wasn’t going anywhere.

‘We’ll deal with him later,’ Fleet replied. Harris looked at him pleadingly, and Fleet turned his back, unsure whether to feel pity or disgust.

Sunday 27 October, 11.01 a.m.

The fire in the main building was gathering momentum. Fleet made directly for the flames.

‘Sir?’ said Bevan, running to keep pace. ‘Where are we going?’ The anxiety was palpable in his voice.

As they diverged from the main stream of people, the space around them began to open up, but the wind was funnelling thick grey plumes into their eyes. Fleet had to pause and wait for the smoke to clear. ‘There,’ he said. ‘That way.’ He pointed to the archway on the southern side of the building that would lead them into the quad.