"I'm you, Charles," the newcomer confirmed. His voice dropped into a stage-whisper. "From the future!"
Charles was simply agog. Oh yes, he'd been musing on the possibilities of time travel for the past year, but at this stage it was more of an intellectual exercise than anything else. Most of his fellow engineers at the conference had laughed and assured him that the premise was an impossibility -- that time travel violated causality, that even the concept itself could not be approached without courting irresolvable paradox -- but Charles had always been fond of thought-exercises. He had, of course, daydreamed and fantasized about the possibilities implicit with the creation of such a device -- not only for him, personally, but what it would do to the face of science -- but he was years away from a working model.
"This isn't possible!" Charles drew back, tipping over the chair he'd been sitting in and crossing an arm across his face. "I haven't even... I mean, it's nothing but idle fancy for now..."
"It works!" his future self repeated. "One year from now you construct a prototype time machine in time for the World Expo here in London. Your work has a tremendous impact - but bear with me, Charles, I cannot reveal to you too much of the future, for both our sakes."
"Causality," Charles nodded.
"It's dangerous. Very dangerous. Even meeting with you like this is a tremendous risk, but it's one I am compelled to take."
"Then why are you here?" Charles righted the fallen chair and set about pouring a cup of tea for his visitor. Chamomile was calming, and both he and... the other him... looked like they needed its influence.
"It's no simple task to relay my purpose without revealing too much," Future-Charles faltered. "I'm not sure exactly how to say this--"