In that impassive colourless man, with his straw hat and his butterfly-net, I seemed to see something terrible--a creature of infinite patience and craft, with a smiling face and a murderous heart.
"It is he, then, who is our enemy--it is he who dogged us in London ?" "So I read the riddle." "And the warning--it must have come from her!" "Exactly." The shape of some monstrous villainy, half seen, half guessed, loomed through the darkness which had girt me so long.
"But are you sure of this, Holmes?
How do you know that the woman is his wife ?" "Because he so far forgot himself as to tell you a true piece of autobiography upon the occasion when he first met you, and I dare say he has many a time regretted it since.

He was once a schoolmaster in the north of England.

Now, there is no one more easy to trace than a schoolmaster.

There are scholastic agencies by which one may identify any man who has been in the profession.

A little investigation showed me that a school had come to grief under atrocious circumstances, and that the man who had owned it--the name was different--had disappeared with his wife.