"Tomorrow," Mary said. There was something about the tone of her voice that worried me. She had been standing in front of the door, staring at it since breakfast. The door had a large '7' painted on it; otherwise it was exactly the same as the six previous doors we had passed through.

Rob turned over in his bunk. "What do you mean?"

"Tomorrow will be our last day," Mary replied. "Have you forgotten?"

"You've become obsessed with this," Rob said, then turned his back to the rest of us.

I went over to Mary and put a hand on her arm, hoping that she would listen. "You need to calm down," I said gently. "Rob's right - there's nothing you can do."

Mary glared at me. "How can you say that?" she began. "We've been going through this - this process for the last week. Every day there's some new rule we've got to obey, some new task we've got to complete. And for what? They won't tell us!" She jabbed a finger at the mirrored hemisphere in the middle of the ceiling. "They watch us all the time! Judging us! Punishing us!"

She pulled herself free of my grasp and ran into the centre of the room., directly under the housing for the cameras. Then she turned her face upwards and began to scream: "I don't care any more! I've had enough! I want out - you hear me? I want out!"

I leapt towards her, hoping to silence her. It was too late. They had heard her. There was a hum, and a distorted voice came from a concealed speaker. "Subject six has exercised their right to discontinue their participation. Subject six shall be removed."

I stopped, then took a step away from Mary. I didn't want to share her fate - but I didn't want to just let her go. We had been in this place for a week and gone through so much. "Please," I said to our unseen observers. "She didn't mean it! She takes it back!" I looked pleadingly at Mary. "Tell them! They'll listen."

Mary smiled at me. "No. I want to go. They won't be able to do anything more to me. I've made my choice."

A panel in the wall slid aside. Four figures dressed in riot armour and masks, carrying metre-long batons walked through the opening. Mary raised her arms in surrender. "Don't worry. I'll come quietly." She gave me one last look as the guards surrounded her. "Maybe I'll see you tomorrow?"

The panel closed behind her. Now there was only Rob and myself left.

"Until tomorrow," I whispered.