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 However, the proposal was rejected, and Gatiss was told that there was no available slot or budget. In order to make the film understandable to a general audience, not all personnel involved in the creation of "Doctor Who" are represented. For example, the role of original story editor David Whitaker is merged with that of associate producer Mervyn Pinfield; co-creator Donald Wilson and writer C.E. Webber are also excluded. Part of the production involved the recreation of scenes from the classic series, including missing episodes such as "Marco Polo". Gatiss also had ambitions to recreate the death of Sara Kingdom