Body on Baker Street is the second book in the Sherlock Holmes Bookshop Mystery series. In the tradition of the genre, you don't need to have read the first book to enjoy this one. There is some major character backstory referenced throughout the book, but none of it is necessary to enjoying the story or understanding the characters.
"When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." -- Sir Arthur Conan Doyle, The Case-Book of Sherlock Holmes