Screenwriters Michael Robert Johnson, Anthony Peckham, and Simon Kinberg whittle the Holmes character down to the basics, reasonably expand him using some of Doyle's background information to give him a slight action hero edge, develop
a pretty crackerjack story involving the occult and a plan to recreate the Gunpowder Plot using a Victorian - style chemical weapon, and read between the lines of the Holmes / Watson dynamic enough to make us read further between the lines.