The first episode, a 60-minute special, premiered on 1 January 2007. The following first series comprised five two-part stories (10 episodes)[1] and aired between 24 September to 19 November 2007.[2] The following three series, Series 2-4, each consisted of six two-part serials[3] and aired annually between 29 September–8 December 2008, 15 October–20 November 2009 and 11 October–16 November 2010, respectively. A fifth series of twelve episodes (6 two-part serials) was commissioned for broadcast in 2011,[4] but only the first three serials were completed prior to the death of Elisabeth Sladen, the series' lead actress.[5] They aired between 3–18 October 2011.