We stopped, gasping for breath.

‘We must go back, Vic!’

She pushed away from me and began to stagger back the way we had come. I stumbled after her, jerked her round.

‘Don’t act the fool, Paula! Now, come on. You’re getting into a panic.’

‘I know,’ She clung to me. ‘I can’t help it. It’s this awful darkness.’

I could feel her trembling against me.

‘Let’s sit down for a moment. We’re going to get out of this; only, you’ve got to keep calm.’

We sat down, and immediately discovered the air was a lot better near the floor of the tunnel. I pushed her flat and lay beside her.

After a few minutes the tightness around my chest and the weights around my limbs went away.

‘This is better.’