He was so subtle that he hid the vast range of his powers behind an appearance of commonplaceness.
Wilton Barnstable never disguised himself, in the ordinary sense of the term.

That is, he never resorted to false whiskers or wigs or obvious tricks of that sort.
But if Wilton Barnstable were to walk into a convention of blacksmiths, let us say, he would quite escape attention.

For before he had been ten minutes in that gathering he would become, to all appearances, the typical blacksmith.

If he were to enter a gathering of bankers, or barbers, or bakers, or organ grinders, or stockbrokers, or school-teachers, a similar thing would happen.

He could make himself the composite photograph of all the individuals of any group.