Michael covered the ground quickly – he was tall, so his paces were much longer than mine. At points I had to trot to keep him in sight, ducking behind bushes from time to time in case he turned around. When we reached the barbed wire near Spooky Joe’s cottage, I stopped and stared. I could still see the neatly snipped ends where Michael had cut Mags free. How stupid I had been! Why would anyone go wandering over the clifftops so early in the morning with a pair of wire cutters in their pocket unless they were up to no good? Yet we hadn’t suspected a thing! I turned around, scanning the path and the clifftop for Michael’s figure, but he had completely vanished from sight.

Up there on the south cliff, there were only two ways he could have vanished so quickly, and it was pretty unlikely that Michael Baron had spontaneously thrown himself off the cliff . . . So that left only one option. He must have taken the tunnel.

Mags.

It was then that I realized I must have left the torch at the Castle when I went back to lock the door. I had never been up or down the tunnel without one. Under these circumstances – completely alone, chasing a criminal whom I knew to be armed with a sharp tool – bathed in the odd light of the gathering clouds, I was frankly surprised that I was still managing to put one foot in front of the other. I approached the old lookout tower and the entrance to the tunnel. I squatted down. ‘You’d better be grateful for this, Mags,’ I whispered under my breath. ‘I might be about to save your life.’ Then I launched myself into the darkness.

It was terrifying. A hellish helter-skelter through absolute darkness, like falling through a nightmare – squeezing and twisting, then slipping blindly while unknown things scratched my face and tore at my hair – down, down, down I fell, deeper into the earth. I may have been the one chasing, rather than being chased, but that didn’t make me feel any less like a helpless creature, like something’s prey. My feet and hands felt the change from loose soil to smooth chalk as I skidded from the upper burrow into the carved-out passage below. I slithered down a steep slope and the blackness was suddenly diluted into a dull, grey haze. The cave at last.

There was no sign of Michael, but my sister was awake and sitting up at the very front of the cave, staring out through the skull’s left eyehole.

‘Mags!’ I panted. ‘Are you all right?’

‘I’m fine, Petra – where on earth have you been?’

‘I had to go back to the lighthouse.’

‘Why—?’

‘It doesn’t matter now. Mags – did Michael Baron come through here?’

She stared at me.