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
Space and Time (Doctor Who) TARDIS suddenly shakes and the lights go out. The Doctor asks Rory if he dropped a thermal coupling, which Rory admits to and apologises for doing. Amy then apologises as well and, at the Doctor's confusion, explains that Rory was looking up her skirt through the glass floor when he dropped the thermal coupling. The Doctor then notes that they have landed through "emergency materialisation" which should have landed the TARDIS in the safest space available. The lights come on, revealing another TARDIS inside the control room — the TARDIS has materialised inside itself. The Doctor experimentally walks through the