This is a collection of short stories in which Sherlock Holmes and Dr. Watson find themselves battling Lovecraftian horrores, with many "My God! The Necronomicon!" moments. The stories are a bit patchy and suffer badly from the Stupid-Watson approach used by bad Conan Doyle adapters. One particularly rubbish piece is a story called 'A Study In Emerald' by Neil Gaiman; it managed to bag a Hugo award, suggesting that they will throw a prize to any old crap if it's written by someone famous.
There are some good stories in here, though, and the general sense of the volume is fundamentally enjoyable. John Pelan's 'The Mystery of the Worm' is impressive for its use of the sheer scary awesomeness of the Lovecraftian world, the sense that there are some forces best not tampered with; it also features Fu Manchu as an unnamed off screen minor character. Barbara Hambly's 'The Adventure of the Antiquarian's Niece' also manages to combine the genres well, and may yet find itself adapted into a Cthulhu Gaslight scenario.