In another he had slipped to the rear of the hall--somewhere there, from the hall itself, from one of the rear rooms, there must be an exit to the fire escape.

To attempt to leave by the front way was certain capture.
They were yelling, shouting down now through the sky-light above, as Jimmie Dale softly raised the window sash at the rear of the hall.

The fire escape was there.

Shouts from along the corridor, from the tenement dwellers who had been crowding their neighbours' rooms, craning their necks probably from the front windows, answered the shouts now from the roof and the skylight; doors opened; forms rushed out--but it was dark in the corridor, only a murky yellow at the upper end from the opened doors.
Jimmie Dale slipped through the window to the fire escape, and, working cautiously, silently, but with the speed of a trained athlete, made his way down.

At the bottom he dropped from the iron platform into the back yard, ran for the fence and climbed over into a lane on the other side.
And then, as he ran, Jimmie Dale snatched the mask from his face and put it in his pocket.