"Never saw him before. Why?"

"He tipped me with a dollar bill when he got off. Later, I looked
closely at it. I do not like it."

He showed it to me, and I didn't blame him. It was marked _One Dollar_,
and _United States of America_, but outside that there wasn't a thing
right about it. One side was gray, all right, but the other side was
green. The picture wasn't the right one. And there were a lot of other
things about it, some of them absolutely ludicrous. It wasn't
counterfeit--it wasn't even an imitation of a United States bill.

And then it hit me, like a bullet in the chest. Not a bill of _our_
United States. No wonder he had been so interested in whether our
scientists accepted the theory of other time dimensions and other worlds
of alternate probability!

On an impulse, I got out two ones and gave them to the porter--perfectly
good United States Bank gold-certificates.

"You'd better let me keep this," I said, trying to make it sound the way
he'd think a Federal Agent would say it. He took the bills, smiling, and
I folded his bill and put it into my vest pocket.

"Thank you, sir," he said. "I have no wish to keep it."

Some part of my mind below the level of consciousness must have taken
over and guided me back to the right car and compartment; I didn't
realize where I was going till I put on the light and recognized my own