Doctor Who (series 4) Astrid Peth, who died during the events of the episode. The companions in the regular series had all been in the lead companion role previously: the primary role of Donna Noble, who was introduced in "The Runaway Bride", was played by Catherine Tate for all thirteen episodes. Her return was announced by the BBC on 3 July 2007. Freema Agyeman, who portrayed the Doctor's companion Martha Jones in series three, returned for "The Sontaran Stratagem", "The Poison Sky", "The Doctor's Daughter", "The Stolen Earth" and "Journey's End". Billie Piper, who played Rose Tyler from the first episode of the new
Doomsday (Doctor Who) the alternate universe Pete Tyler, who tells him that after he left the Cybermen were sealed in their factories while humanity decided what to do with them. In the meantime, the Cybermen vanished and the breach began causing unprecedented global warming on the parallel Earth, which the Doctor theorises is the start of the process that will lead to both planets falling into the Void. Pete demands the Doctor seal the breach before his Earth is destroyed. Meanwhile, Rose deduces that she and Mickey were kept alive because their touch can activate the Genesis Ark. Dalek Sec explains that they