"McCarthy. Hey! What do you mean—'this other McCarney?' I'm the only McCarthy—only Gooseneck McCarthy, anyway. If you send a dozen different guys out to do the same job...."
"I didn't send anyone but you. Don't you understand what happened? You went back into the Cretaceous to move a rock. You returned to the present—and, as you say, found me in somewhat unfortunate circumstances. You returned to the past to undo the damage, to approximately the same spot in space and time as before—it could not be exactly the same spot because of a multitude of unknown factors and because of the inescapable errors in the first time machine. Very well. You—we'll call you You I—meet You II at the very moment You II is preparing to move the rock. You stop him. If you hadn't, if he hadn't been interrupted in any way and had shifted that stone, he would have been You I. But because he—or rather you—didn't, he is slightly different from you, being a You who has merely made one trip into the past and not even moved the rock. Whereas you—You I—have made two trips, have both moved the rock yourself and prevented yourself from moving it. It's really very simple, isn't it?"
McCarthy stroked his chin and sucked in a great gasp of air. "Yeah," he mumbled wildly. "Simple ain't the word for it!"
The professor hopped into the machine and began preparing it for another trip. "Now as to what happened to me. Once you—You I again—prevented You II from moving that rock, you immediately precipitated—not so much a change as a—an unchange in my personal situation. The rock had not been shifted—therefore, I had not been married, was not married, and, let us hope, will never be married. I was also no longer bald. But, by the very fact of the presence of the two You's in the past, by virtue of some microscopic form of life you killed with your breath, let us say, or some sand you impressed with your feet,—sufficient alterations were made right through to the present so that my name was (and always had been!) Roodles and your name—"
"Is probably MacTavish by now," McCarthy yelled. "Look prof, are you through with the machine?"
"Yes, it's all ready." The professor grimaced thoughtfully. "The only thing I can't place is what happened to that camera you said I took from you. Now if You I in the personification of You II—"
McCarthy planted his right foot in the small of the little man's back and shoved. "I'm gonna get this thing settled and come back and never, never, never go near one of these dinguses again!"
He yanked at the chronotransit. The last he saw of the professor was a confused picture of broken glassware, tangled electrical equipment and indignantly waving white hair.
This time he materialized at the very edge of the beach. "Gettin' closer all the time," he mumbled as he stepped out of the housing. Now to hand over the note, then—