In some ways English author Anthony Horowitz was presented with a gift when he was invited to write the first official Sherlock Holmes novel since the Arthur Conan Doyle era.
This gift comprised: two of the most clearly defined heroes of English literature; a choice of atmospheric settings (he opted for the gas-lit, fog-coated merciless London winter of 1890); the blessing of the Conan Doyle estate (and thus a guaranteed following from fans); and a poisoned chalice.
Modern recreations of classic books have a tendency to go horribly wrong in a very high-profile way. Take Scarlett, Alexandra Ripley's widely panned 1991 sequel to Gone with the Wind, and Pemberley, Emma Tennant's dire 1993 follow-up to Pride and Prejudice.
The problem with most sequels is that the author must rip apart the carefully constructed resolution of the original to insert a new conflict in order to get the plot going again.
Horowitz, of course, didn't have that problem with the Sherlock Holmes canon, since it was mostly a collection of short stories that were largely self-contained, with characters who developed little over the lifetime of the series. He didn't have to bring Holmes back from retirement - or from the dead (as Conan Doyle did himself when he decided to renew the series in 1903 after having killed off the detective 10 years earlier).
Horowitz just needed to slide another adventure into the career of Sherlock Holmes, being careful not to mess up the continuity of the existing tales.