 The Doctor 's former companions Captain Jack Harkness , Martha Jones , Sarah Jane Smith , and Rose Tyler — who have all encountered the Daleks before — hide in various places : Jack takes refuge in the Torchwood Hub ( 51 ° 27 ′ 50 ″ N 3 ° 09 ′ 51 ″ W ) with his team ; Martha uses Project Indigo — an experimental teleport device scavenged from the Sontarans — to escape UNIT New York with the " Osterhagen Key " , a device that activates a defensive last resort nuclear weapons system ; Sarah Jane stays in her home with her son Luke Smith and supercomputer Mr Smith ; and Rose tracks down Noble 's mother and grandfather . They are contacted by former Prime Minister Harriet Jones through a secret " subwave network " designed by Mr Copper — a humanoid alien who met the Doctor in " Voyage of the Damned " — to contact the Doctor 's companions in an emergency . They attempt to contact the Doctor by amplifying the sub @-@ wave signal ; Sarah uses Mr Smith 's computing power and Torchwood manipulates the spatial @-@ temporal rift in Cardiff . The Doctor and the Daleks receive the transmission and trace the signal : the Daleks kill Harriet Jones ; and the Doctor is able to locate Earth in a temporally desynchronised pocket universe . 
