Rose tells the Doctor about her father and the stories her mother told her about how he died alone when she was a baby.  She wants to be there when he dies so that he doesn't die alone.  When she sees him die she can't handle it and runs away.  The Doctor, bending the laws of time, allows her a second chance but this time she saves her father causing a serious breach in the time continuum.  Because of this, reapers (cosmic bacteria) attempt to take advantage of this and clean the wound in time by destroying everything on Earth.  The Doctor and Rose hide out with her parents and the wedding party that they were attending in an old church.  When Rose holds herself as a young baby she causes a paradox and the Doctor is consumed by a reaper trying to save her.  Rose's father realizes why these horrible things are happening and sacrifices himself in order to put things right.  Rose is there this time when he dies and she and the Doctor leave in the TARDIS afterward.  Time has been changed slightly as Rose now remembers her mother telling her about a mysterious woman that was there when her father died.