Steven Moffat works the same magic for Robert Louis Stevenson that he worked for Sir Arthur Conan Doyle with Sherlock.  Absolutely magnificent, with tour de force performances by James Nesbitt.  Its only flaw: trying to set things up for a second series that was never commissioned.  There are times when a series (or season, as we say in the US) should stand alone, and this is one of them.  James Nesbitt continues to impress the pants off me.