Sherlock Holmes and the Rule of Nine is a book by Barrie Roberts and was published in 2003.
Summary[]
When a series of bizarre accidents befall small shopkeepers who have recently taken precautions to protect their premises, Sherlock Holmes is the first to discern a pattern, to the befuddlement of his most loyal friend. It seems someone is running a protection racket, and more, murder is involved, so Holmes teams up with a New York detective who has travelled to London to get to the bottom of the Rule of Nine.