"Not a clue," the Doctor said. He beamed madly at the other man. It had been a good long while since he'd had someone to bounce theories off of and be generally magnificent around. It would be good for him.

And besides, Alan was wearing the right sort of shoes for the Doctor's life.

"Best way to find out is to follow it to the source, which looks like it would be..." He pointed towards the opposite end of the Mall.

"This way!"