But Gatewood, on the sidewalk under the lamplight, was still laughing as Kerns drove away, for he had recognized in the cab driver a man he had seen in Mr. Kern’s office, and he knew that the Tracer of Lost Persons had Kerns already well in hand.

The hansom drove on through the summer darkness between rows of electric globes drooping like huge white moon flowers from their foliated bronze stalks, on up the splendid avenue, past the great brilliantly illuminated hotels, past the white cathedral, past clubs and churches and the palaces of the wealthy; on, on along the park wall edged by its double rows of elms under which shadowy forms moved—­lovers strolling in couples.

“Pooh,” sniffed Kerns, “the whole world has gone love mad, and I’m the only sane man left.”

But he leaned back in his cab and fell a-thinking of a thin girl with red hair and great gray eyes—­a thin, frail creature, scarcely more than a child, who had held him for a week in a strange sorcery only to release him with a frightened smile, leaving her indelible impression upon his life forever.

And, thinking, he looked up, realizing that the cab had stopped in East Eighty-third Street before one of a line of brownstone houses, all externally alike.

Then he leaned out and saw that the house number was thirty-eight.  That was the number of the Lees’ house; he descended, bade the cabman await him, and, producing his latch key, started up the steps, whistling gayly.

But he didn’t require his key, for, as he reached the front door, he found, to his surprise and concern, that it swung partly open—­just a mere crack.

“The mischief!” he muttered; “could I have failed to close it?  Could anybody have seen it and crept in?”

He entered the hallway hastily and pressed the electric knob.  No light appeared in the sconces.

“What the deuce!” he murmured; “something wrong with the switch!” And he hurriedly lighted a match and peered into the darkness.  By the vague glimmer of the burning match he could distinguish nothing.  He listened intently, tried the electric switch again without success.  The match burned his fingers and he dropped it, watching the last red spark die out in the darkness.

Something about the shadowy hallway seemed unfamiliar; he went to the door, stepped out on the stoop, and looked up at the number on the transom.  It was thirty-eight; no doubt about the house.  Hesitating, he glanced around to see that his hansom was still there.  It had disappeared.

“What an idiot that cabman is!” he exclaimed, intensely annoyed at the prospect of lugging his heavy suit case to a Madison Avenue car and traveling with it to Harlem.

He looked up and down the dimly lighted street; east, an electric car glided down Madison Avenue; west, the lights of Fifth Avenue glimmered against the dark foliage of the Park.  He stood a moment, angry at the desertion of his cabman, then turned and reentered the dark hall, closing the door behind him.