The Doctor dug into his pocket and produced the yo-yo. He tossed it out into the board, and the whole thing electrified.

"Oh, now that's clever," the Doctor enthused. "A checkerboard puzzle. The question is, which ones do we step onto?"

He was very, very good at puzzles and, before he could really think about it, he found he was really glad he was the one working on this. He was, naturally, brilliant, and there wasn't a riddle in the known universe he couldn't work out in time.

The overconfidence fueling him, he grasped Jack by the arm. "I bet we could just jump it."