as it was the only one in sight I concluded that it must
be the same which Sylvia had taken from the hotel.

Some distance further on I walked, when, before me, I recognized her
neat figure, and almost a moment afterwards saw her disappear into a
large doorway which was in complete darkness--the doorway of what
seemed to be an untenanted house.

I halted quickly and waited--yet almost ashamed of myself for spying
thus.

A moment later I saw that, having believed herself unobserved, she
struck a match, but for what reason did not seem apparent. She
appeared to be examining the wall. She certainly was not endeavouring
to open the door. From the distance, however, I was unable to
distinguish very plainly.

The vesta burned out, and she threw it upon the ground. Then she
hurriedly retraced her steps to where she had left her cab, and I was
compelled to bolt into a doorway in order to evade her.

She passed quite close to me, and when she had driven away I emerged,
and, walking to the doorway, also struck a light and examined the same
stone wall. At first I could discover nothing, but after considerable
searching my eyes at last detected a dark smudge, as though something
had been obliterated.

It was a cryptic sign in lead pencil, and apparently she had drawn her
hand over it to remove it, but had not been altogether successful.
Examining it closely, I saw that the sign, as originally scrawled upon
the smooth stone, was like two crescents placed back to back, while
both above and below rough circles had been drawn.

The marks had evidently some prearranged meaning--one which she
understood. It was a secret message from her father, without a doubt!

At risk of detection by some agent of police, I made a further close
examination of the wall, and came upon two other signs which had also
been hurriedly obliterated--one of three double triangles, and another
of two oblongs and a circle placed in conjunction. But there was no
writing; nothing, indeed, to convey any meaning to the uninitiated.

The wall of that dark entry, however, was no doubt the means of an
exchange of secret messages between certain unknown persons.

The house was a large one, and had been let out in flats, as were its
neighbours; but for some unaccountable reason--perhaps owing to a law
dispute--it now remained closed.

I was puzzled as to which of the three half-obliterated signs Sylvia
had sought. But I took notice of each, and then walked bac