At last I said: "We're moving along real nice now." No answer. I tried again: "Evidently that secret experiment that destroyed existence was based on this FitzJohn's erroneous theory, eh?" The C-S stirred and said: "What? Oh--Yes, Carmichael, quite right." In low tones the controller said: "I wish it hadn't happened. He was a nice-looking youngster, that Wilder--promising." I said: "In the name of heaven, sir, it's not going to happen if we pull ourselves together. If we can locate the very beginning and change it, he'll probably marry the girl and live happily ever after." "Of course--" The controller was confused. "I hadn't realized." I said: "We've got to hunt back a lot more and locate this FitzJohn. He seems to be the key man in this puzzle." * * * * * And how we searched. Boys, it was like working a four-dimensional jig saw, the fourth dimension in this case being time. We located a hundred universities that maintained chairs and departments exclusively devoted to FitzJohn's mathematics and theories. We slipped back a hundred years toward the present and found only fifty and in those fifty were studying the men whose pupils were to fill the chairs a century later. Another century back and there were only a dozen universities that followed the FitzJohn theories. They filled the scientific literature with trenchant, belligerent articles on FitzJohn, and fought gory battles with his opponents. How we went through the libraries. How many shoulders we looked over. How many pages of equations we snap-photographed from the whirling octahedron for future reference. And finally we worked our way back to Bowdoin College, where FitzJohn himself had taught, where he worked out his revolutionary theories and where he made his first converts. We were on the home stretch. FitzJohn was a fascinating man. Medium height, medium color, medium build--his body had the rare trick of perfect balance. No matter what he was doing, standing, sitting, walking, he was always exquisitely poised. He was like the sculptor's idealization of the perfect man. FitzJohn never smiled. His face was cut and chiseled, as though from a roughish sandstone; it had the noble dignity of an Egyptian carving. His voice was deep, unimpressive in quality, yet unforgettable for the queer, intense stresses it laid on his words. Altogether he was an enigmatic creature. He was enigmatic for another reason, too, for although we traced his career at Bowdoin backward and forward for all its forty years, although we watched him teach the scores and scores of disciples who afterward went out into the scholastic world to take up the fight for him--we could never trace FitzJohn back into his youth. It was impossible to pick him up at any point earlier than his first appearance on the physics staff of the college. It seemed as though he were deliberately concealing his identity.