"You've got to be joking."
"Afraid not," the Doctor grimaces, squatting and looking down tunnel ahead. The ceiling is barely high enough for us to crawl through. "We've got to find out what's down there. Quicker we get down there, the quicker we come back up."
We start the long crawl through the tunnels. As we lose the light behind us, the Doctor takes two head-torches from her coat and hands one to me. My breathing becomes shallow as I feel the walls closing in around us, and very soon I have to drop behind the Doctor.
As my hands and knees begin to hurt, the tunnel widens again, and the ceiling suddenly gets high enough for us to stand.
"Well done, Danni," the Doctor says, clapping me on the back. "I'm dead proud of you. Now, let's see what's down here..." She fishes a torch from her pocket, and shines it around while I do the same with my phone.
A heavy clunking sound echoes around the tunnel. I look back at the Doctor, my eyes wide. "What was that?"
She doesn't reply, and seconds later the wall begins to move towards us. "Quick, back this way," the Doctor instructs, and I stumble backwards. But as we near the other wall, it too starts to move towards us. The entrance to the tunnel disappears as the wall moves past it, blocking off our only escape.
"There goes our exit," I say weakly. "How long before it crushes us?"
The Doctor spins around and walks back to me, grabbing my hand, grounding me. "I am not going to let that happen," she says firmly, looking me in the eye. "You have to trust me." I look back at her, aware the walls are less than five meters apart now, and nod. She smiles and lets go, turning to where a red light is flashing above us. The Doctor raises her sonic screwdriver towards it, and in the next moment the walls stop.
I let out a sigh of relief. To our right, a gap appears in the wall which the Doctor walks towards before looking back at me. "Ready?"