IT was after midnight, October 8.  Pendrake walked, head bent into a strong east wind along a well-lighted street in the Riverdale section of New York City.  He peered at the numbers on the houses as he pressed by: 418, 420, 432.

Number 432 was the third house from the corner, and he walked on past it to the light post.  Back to the wind, he stood in the bright glow, once more studying his precious list - a final verification.  His original intention had been to investigate every one of the seventy-three eastern Americans on that list, starting with the A's.  On second thought, he had realized that scientists of firms like Westinghouse, the Rockefeller Foundation, private laboratories with small means, and physicists and professors who were carrying on individual research were the least likely candidates, the former because of the impossibility of secrecy, the latter because that engine must have plenty of money behind it.  Which left twenty-three private foundations.

Even that was a huge undertaking for one man; the chance of being caught put a strain on his face and into the muscles of his body and tightened up that growing arm.  And this was only his eleventh investigation.  The others had proved as fruitless as they were dangerous.

Pendrake put his list away and sighed.  There was no use delaying.  He had come down the alphabet to the Lambton Institute, whose distinguished executive physicist, Dr. McClintock Grayson, lived in the third house from the corner.

He reached the front door of the darkened residence and experienced his first disappointment.  In a dim way, he had hoped the door would be unlocked.  It wasn't, and that meant that all the doors he had opened in his life without ever noticing they were locked would now have to be precedents, proofs that a Yale lock could be broken silently.  It seemed different, doing it on purpose, but he tensed himself and gripped the knob.  The lock broke with the tiny click of metal that has been abruptly subjected to unbearable pressure.

In the inky hallway Pendrake stood for a moment, listening.  But the only sound was the pounding of his heart.  He went forward cautiously, using his flashlight as he peered into doors.  Presently he verified that the study must be on the second floor.  He took the stairs four at a time.

The hallway of the second floor was large, with five closed doors and two open ones leading from it.  The first open door led to a bedroom, the second into a large, cozy room lined with bookshelves.  Pendrake sighed with relief as he tiptoed into it.  There was a desk in one corner, a small filing cabinet, and several floor lamps.  After a swift survey, he closed the door behind him and turned on the trilight beside the chair next to the desk.