Rae is ignoring Jemma's staring, and trying to ignore the way even the uneven drip..............drip of water droplets from somewhere in the darkness are making her tense up.

"I vote we head that way," she says. "Uphill."

That sound comes again - a far-off, echoing sound, like the enraged bellow of an animal. But the passageways make it impossible to tell which way the sound is coming from.

"Okay, I know it's not my imagination now. Let's go."