The Final Page of Baker Street by Daniel D Victor (MX; £8.99) concerns the last ‘boy in buttons’ to serve at 221B before Sherlock Holmes’s retirement. Although like his predecessors he’s known as ‘Billy’, he is actually a rather unruly adolescent Irish-American pupil at Dulwich College. His name is Raymond Chandler, and he has literary ambitions. Add murder, suicide, Colonel Moran and Youghal of the CID, and you have an exciting, intelligent, literate mystery.