Kinnison galloped across the alley and opened the door of a small garage, revealing a long, squat motorcycle. Two deft passes of his hands and two of his three spotlights were no longer white--one flashed a brilliant purple, the other a searing blue. He dropped a perforated metal box into a hanger and flipped a switch--a peculiarly-toned siren began its ululating shriek. He took the alley turn at an angle of forty-five degrees; burned the pavement toward Diversey. The light was red. No matter--everybody had stopped--that siren could be heard for miles. He barreled into the intersection; his step-plate ground the concrete as he made a screaming left turn. A siren--creeping up from behind. City tone. Two red spots--city cop--so soon--good! He cut his gun a trifle, the other bike came alongside. "Is this IT?" the uniformed rider yelled, over the coughing thunder of the competing exhausts. "Yes!" Kinnison yelled back. "Clear Diversey to the Outer Drive, and the Drive south to Gary and north to Waukegan. Snap it up!" The white-and-black motorcycle slowed; shot over toward the curb. The officer reached for his microphone. Kinnison sped on. At Cicero Avenue, although he had a green light, traffic was so heavy that he had to slow down; at Pulaski two policemen waved him through a red. Beyond Sacramento nothing moved on wheels. Seventy ... seventy five ... he took the bridge at eighty, both wheels in air for forty feet. Eighty five ... ninety ... that was about all he could do and keep the heap on so rough a road. Also, he did not have Diversey all to himself any more; blue-and-purple-flashing bikes were coming in from every side-street. He slowed to a conservative fifty and went into close formation with the other riders. The H-blast--the city-wide warning for the planned and supposedly orderly evacuation of all Chicago--sounded, but Kinnison did not hear it. Across the Park, edging over to the left so that the boys going south would have room to make the turn--even such riders as those need _some_ room to make a turn at fifty miles per hour! Under the viaduct--biting brakes and squealing tires at that sharp, narrow, right-angle left turn--north on the wide, smooth Drive! That highway was made for speed. So were those machines. Each rider, as he got into the flat, lay down along his tank, tucked his chin behind the cross-bar, and twisted both throttles out against their stops. They were in a hurry. They had a long way to go; and if they did not get there in time to stop those trans-polar atomic missiles, all hell would be out for noon.