the
afternoon, and so overcast the sky that in many rooms the gas was lit
and the curtains drawn.

The girl, apparently from observing the daily progress of the sun, had
written she was on the west side of the street and, she believed, in
an upper story. The man who picked up the note had said he had found
it opposite the houses in the middle of the block. Accordingly, Ford
proceeded on the supposition that the entire east side of the street,
the lower stories of the west side, and the houses at each end were
eliminated. The three houses in the centre of the row were outwardly
alike. They were of four stories. Each was the residence of a physician,
and in each, in the upper stories, the blinds were drawn. From the front
there was nothing to be learned, and in the hope that the rear might
furnish some clew, Ford hastened to Wimpole Street, in which the houses
to the east backed upon those to the west in Sowell Street. These houses
were given over to furnished lodgings, and under the pretext of renting
chambers, it was easy for Ford to enter them, and from the apartments
in the rear to obtain several hasty glimpses of the backs of the three
houses in Sowell Street. But neither from this view-point did he gather
any fact of interest. In one of the three houses in Sowell Street
iron bars were fastened across the windows of the fourth floor, but in
private sanatoriums this was neither unusual nor suspicious. The bars
might cover the windows of a nursery to prevent children from falling
out, or the room of some timid householder with a lively fear of
burglars.

In a quarter of an hour Ford was again back in Sowell Street no wiser
than when he had entered it. From the outside, at least, the three
houses under suspicion gave no sign. In the problem before him there was
one point that Ford found difficult to explain. It was the only one that
caused him to question if the letter was genuine. What puzzled him was
this: Why, if the girl were free to throw two notes from the window, did
she not throw them out by the dozen? If she were able to reach a window,
opening on the street, why did she not call for help? Why did she not,
by hurling out every small article the room contained, by screams, by
breaking the window-panes, attract a crowd, and, through it, the police?
That she had not done so seemed to show that only at rare intervals
was she free from restraint, or at liberty to enter the front room that
opened on the street. Wo