"In Mr Cecil’s illuminating background notes, he describes the Doctor as follows:
“A frail old man lost in space and time. They give him this name because they don’t know who he is. He seems not to remember where he has come from: he is suspicious and capable of sudden malignance; he seems to have some undefined enemy; he is searching for something as well as fleeing from something. He has a ‘machine’ which enables them to travel together through time, through space and through matter."
“Steven Moffat says: “The three stories will be called A Scandal In Belgravia, The Hounds Of Baskerville and The Reichenbach Fall.”
Mark Gatiss reveals that when it came to sharing the writing responsibilities, Steven chose to do the twisted love story (Scandal) while he chose the Gothic horror (Baskerville) and Stephen Thompson (Silk, Doctor Who) is writing the thrilling finale (Reichenbach).”
-BBC Press Office