 " A Scandal in Belgravia " , written by Steven Moffat and directed by Paul McGuigan , was first broadcast on 1 January 2012 . Loosely based on " A Scandal in Bohemia " , the episode depicts Holmes 's quest to retrieve compromising photos of a minor royal held on the camera phone of Irene Adler ( Lara Pulver ) , a ruthless and brilliant dominatrix who also trades in classified information extracted from her rich and powerful clients . 
