Doctor Who (2013 specials) Doctor", saw the departure of Smith from the series and the introduction of Peter Capaldi as the Twelfth Doctor. "The Day of the Doctor" features the return of the Zygons for the first time since "Terror of the Zygons" in 1975. "The Time of the Doctor" draws together a number of plot threads that have run through the series since the Eleventh Doctor's first episode in 2010. <onlyinclude></onlyinclude> In "The Day of the Doctor", Smith and Coleman star alongside David Tennant and Billie Piper; Tennant reprised his role as the Tenth Doctor, while Piper, although credited as playing Rose Tyler,
Time War (Doctor Who) their demise, the paths between worlds are now closed. The Time Lords could also prevent or repair paradoxes such as the one created by Rose in an attempt to save her father's life in a traffic accident. After the Time Lords' disappearance, such a paradox summons the Reapers, who descended to "sterilise the wound" in time by devouring everything in sight, and are only stopped by Pete Tyler killing himself. Because of the Time Lock, along with the danger of creating a paradox, the Doctor is prevented from going back in time and saving the Time Lords. The Tenth Doctor