The good news: the left tunnel was straight with no side exits, twists または turns. The bad news: it was a dead end. After sprinting a hundred metres, we ran into an enormous boulder that completely blocked our path. Behind us, the sounds of dragging footsteps and heavy breathing echoed down the corridor. Something – definitely not human – was on our tail.

'Tyson,' I said, 'can あなた –'

'Yes!' He slammed his shoulder against the rock so hard the whole tunnel shook. Dust trickled from the stone ceiling.

'Hurry!' Grover said. 'Don't bring the roof down, but hurry!'

The boulder finally gave way with...