 Adam Mitchell ( Bruno Langley ) joins the Doctor and Rose as companion at the end of " Dalek " . However , when he tries to smuggle future knowledge from Satellite Five in the year 200 @,@ 000 back to his own time in " The Long Game " the Doctor expels him from the TARDIS . The Doctor is angry at Rose after he takes her to the event of father Pete Tyler ( Shaun Dingwall ) ' s death and she saves his life , causing a paradox . However , when Pete dies to restore the timeline he shows compassion and encourages her to sit by his side as he passes away . After encountering Captain Jack Harkness ( John Barrowman ) ( a con artist and former Time Agent from the 51st century ) in 1941 , the Doctor realises Harkness had caused a deadly nanotechnological plague to sweep through the human race , turning humans into gas @-@ mask zombies . Following the resolution of the situation , Jack prepares to sacrifice himself , but the Doctor saves him and invites him on board the TARDIS . When the Doctor encounters Blon ( Annette Badland ) , the only Slitheen to survive the Downing Street explosion in present @-@ day Cardiff he has doubts over whether or not to send her home to be executed . During this episode the Doctor first notices that he and Rose had kept coming across the words " Bad Wolf " . In the episode " Bad Wolf " the Doctor , Rose and Jack find themselves at the mercy of the Bad Wolf Corporation based on Satellite Five . However , the true enemy is revealed to be the Daleks , the Dalek Emperor having also survived the Time War and had rebuilt the Dalek race . The Doctor sends Rose back to the 21st century to protect her before attempting to destroy the Dalek army . When he realises that doing this would destroy most of planet Earth he is unable to do so , proclaiming he would rather be a coward than a killer . Having absorbed the energies of the time vortex , Rose is able to return to the Doctor and destroy the Daleks . To save Rose from being killed by harbouring the time vortex , the Doctor removes the harmful effects by kissing her . However , the damage to his cells causes him to regenerate and the Tenth Doctor ( David Tennant ) takes his place . 
