More like 3.5, but I'll go with four – for a first novel, The Affair of the Porcelain Dog
is really solid.
An atmospheric mystery set in Victorian London, giving a clear nod to Arthur Conan Doyle, but with enough own character development to be more than a mere pastiche. I enjoyed following 1st-person-narrator Ira Adler, former rent boy and current plaything of a criminal mastermind, running around the more sordid parts of historical London, and watch his personal growth.
No romance, no sex, although it's marketed as m/m romance – when in fact it's a well written mystery, not more, not less.