Prologue

Detective John Masters turned back to question the helpful civilian, but the man was no longer at his side. A grey-coated back was just disappearing into the alley beside the bank. The detective smiled grimly. He knew it was a dead end. He set off in pursuit, he had more than a few questions for that young man. He turned the corner and saw his quarry at the end of the alley. "Police!" he called. "Don't move!"
Then the man disappeared, right before his eyes. One minute he was there, and the next second he wasn't. The alley was empty apart from a few pieces of rubbish, scarcely big enough to hide a rat.