husbands take long and mysterious trips from home--a thousand
exciting and worrying things may happen to the astonishment,
distress, or intense interest of nations, governments,
political parties, or private individuals, which from their
very nature are outside the purview of the regular police.
Here, then, is the field of the secret agent or private
detective, and here, forsooth, is where the detective of
genuine deductive powers and the polished address of the
so-called "man of the world" is required.

There are two classes of cases where a private detective must
needs be used, if indeed any professional assistance is to be
called in: first, where the person whose identity is sought to
be discovered or whose activities are sought to be terminated
is not a criminal or has committed no crime, and second,
where, though a crime has been committed, the injured parties
cannot afford to undertake a public prosecution.

For example, if you are receiving anonymous letters, the
writer of which accuses you of all sorts of unpleasant things,
you would, of course, much prefer to find out who it is and
stop him quietly than to turn over the correspondence to the
police and let the writer's attorneys publicly cross-examine
you at his trial as to your past career. Even if a diamond
necklace is stolen from a family living on Fifth Avenue, there
is more than an even chance that the owner will prefer to
conceal her loss rather than to have her picture in the
morning paper. Yet she will wish to find the necklace if she
can.