That is not Tobias Gregson's way of going to work.

You remember the hat beside the dead man ?" "Yes," said Holmes; "by John Underwood and Sons, 129, Camberwell Road." Gregson looked quite crest-fallen.
"I had no idea that you noticed that," he said.

"Have you been there ?" "No." "Ha!" cried Gregson, in a relieved voice; "you should never neglect a chance, however small it may seem." "To a great mind, nothing is little," remarked Holmes, sententiously.
"Well, I went to Underwood, and asked him if he had sold a hat of that size and description.

He looked over his books, and came on it at once.
He had sent the hat to a Mr.Drebber, residing at Charpentier's Boarding Establishment, Torquay Terrace.

Thus I got at his address." "Smart--very smart!" murmured Sherlock Holmes.
"I next called upon Madame Charpentier," continued the detective.
"I found her very pale and distressed.