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