The Doctor (Doctor Who) Time Lords a fixed number of twelve regenerations, meaning that every Time Lord had a total of thirteen incarnations including the original. The plot of "The Time of the Doctor" involves the Doctor receiving a new cycle of regenerations from the Time Lords before his expected demise, triggering the regeneration into the Twelfth Doctor, played by Peter Capaldi. The origins of the programme were explored in the docudrama "An Adventure in Space and Time" as part of the 50th anniversary celebrations of "Doctor Who", which starred David Bradley as William Hartnell. Although Time Lords resemble humans, their physiology differs in
An Adventure in Space and Time of Castamere". "An Adventure in Space and Time" was released on DVD on 2 December 2013 in the UK. A 3 disc Blu-ray set was released in the US and Canada 27 May 2014. The set includes the feature on Blu-ray, DVD and An Unearthly Child DVD. The special was re-released on DVD and Blu-ray on 8 September 2014 as part of a "50th Anniversary Collectors Boxset" alongside "The Name of the Doctor", "The Night of the Doctor", "The Day of the Doctor", "The Time of the Doctor" and "The Five(ish) Doctors Reboot". Edmund Butt's score was released by Silva