Page "The Adventure of the Creeping Man" Paragraph 13

Holmes has formed a theory that every nine days, Professor Presbury takes some kind of drug which causes the odd behaviour.

Holmes believed that he became addicted in Prague, and is now supplied by this Dorak in London.

Holmes has told Mr. Bennett that he and Watson will be in Camford once again on the next Tuesday.

As is usual with Holmes, he does not explain why.