"Deadlock seal," the Doctor said. "We'll have to wing it. Shouldn't be too hard, though. And we can always call a lifeline."

He pulled out his mobile and gave it a little wave in Jack's direction. "Martha'll help us out. She's handled pop quizzes like this before."

This was better. Running around, death on their heels, preparing to uncover one of the great mysteries of the universe. The Doctor's smile was wide and genuine as he led the way to Section B. He grabbed a door clamp and a small computer, which he tossed to Jack.

"Piece of cake."