 Through exposition, it is revealed that Martha has become a "medical officer" for international paranormal investigations agency UNIT since qualifying as a Doctor of Medicine.Martha briefly joins the Cardiff-based Torchwood Three as its medical officer following the death of Owen Harper (Burn Gorman), but later leaves the organisation in the episode "A Day in the Death" once she is satisfied that Owen is fit to return to duty following his resurrection.Later in the fourth series of "Doctor Who" (2008), Martha returns for a three-episode arc beginning with the two-part story, "The Sontaran Stratagem" and "The Poison Sky", and ending with "The Doctor's Daughter", in which she meets The Doctor's new companion Donna Noble (Catherine Tate); in the first episode, a more assertive and engaged Martha summons The Doctor to Earth to help uncover a plot by the Sontarans.