The Fugitives

Somehow Jeff Engel followed the stranger into another world—among people who hated all aliens. And of course, he was now one himself!
Jeff Engel studied the feverish crowd hurrying through the subway turnstiles. As he checked each passing face against a card-index mind, he smiled to himself. Even when off duty, the habit persisted. There was always the chance he'd spot a face that would fit, one that would close another active file in Missing Persons Bureau.
A mousey little guy slipped through a turnstile and bumped into a fat woman shopper. Engel glanced at the thin apologetic face and then at a briefcase bearing the faded initials, "C. G." As a train rumbled in and the noise of the commuters rose, something glinted at Engel's feet. He bent down, curious. It was a cheap fountain pen inscribed with the same initials. He caught a glimpse of the stranger on the crowded subway stairs.
"Wait a minute, mister!" he yelled. When C. G. didn't turn, Engel hesitated, then pounded up the stairs into dazzling sunlight. He squinted around at people and then over low bushes into the city park where he saw the little fellow walking briskly. Annoyed, Engel trotted down a shady walk, then down a quiet lane and finally reached out to tap his shoulder.
C. G. vanished in thin air. Engel slid to a halt and rubbed his eyes. Fearfully he explored this queer illusion, his hands pawing nothingness. There was a roar like a thousand subway trains, and something invisible and powerful hurled him sprawling. He lay stunned as the noise died away and then sat up to nurse a bruised head.
Someone grabbed his arms, jerked him rudely to his feet, and spun him around. A tall gangling cop glared down at him. "You been drinking?" "W-what?" Engel stammered. Confused, he looked more closely at this man who wore a gray metallic uniform, a glittering badge, and an oddly shaped holster. "I wasn't drinking. Something pushed me."