substitution of lodgers. What I did not foresee is that we
should find a woman, and no ordinary woman, Watson."

"She saw us."

"Well, she saw something to alarm her. That is certain. The
general sequence of events is pretty clear, is it not? A couple
seek refuge in London from a very terrible and instant danger.
The measure of that danger is the rigour of their precautions.
The man, who has some work which he must do, desires to leave the
woman in absolute safety while he does it. It is not an easy
problem, but he solved it in an original fashion, and so
effectively that her presence was not even known to the landlady
who supplies her with food. The printed messages, as is now
evident, were to prevent her sex being discovered by her writing.
The man cannot come near the woman, or he will guide their
enemies to her. Since he cannot communicate with her direct, he
has recourse to the agony column of a paper. So far all is
clear."

"But what is at the root of it?"

"Ah, yes, Watson--severely practical, as usual! What is at the
root of it all? Mrs. Warren's whimsical problem enlarges
somewhat and assumes a more sinister aspect as we proceed. This
much we can say: that it is no ordinary love escapade. You saw
the woman's face at the sign of danger. We have heard, too, of
the attack upon the landlord, which was undoubtedly meant for the
lodger. These alarms, and the desperate need for secrecy, argue
that the matter is one of life or death. The attack upon Mr.