Christina is a companion of the Twelfth Doctor, and the third overall. She meets the Doctor in The Girl and the Monster when he saves her from the clutches of the Slitheen Fell Blotch Dreg, masquerading as the local MP Andrew MacCoffey and also trying to make Christina his bride.
Christina never fully reveals her last name, and simply goes by Christina. She is 26, and works as a secretary in South London for Andrew MaCoffey, who is really the Slitheen Fell Blotch Dreg. Despite being at first frightened and repulsed by Fell Blotch Dreg; she sympathizes with him as a Slitheen purge undergone by the Daleks during the Time War, something the Doctor did not know of. When the Doctor meets Christina he attempts to destroy Fell Blotch, instinctively, but after the Slitheen explains he shows mercy and takes him to a safer place.
Although she lives a rather work-oriented life; Christina seems to recall all the spaceship sightings and events linked with the Doctor on Earth, and recognizes the name Dalek.
Unlike the Doctor's previous female companion Isabella Cartwright, Christina is outgoing and speaks her mind. She is very knowledgeable, and can help the Doctor in many scientific and mechanical situations. Her reaction to the Daleks (The Survival of the Daleks, The New Breed) is at the most terrified, although she does not have any fear standing up to them. The Dalek Pariah likens her to the Doctor's companion Romana. She is extremely resourceful in many situations; and often corrects the Doctor if he does some wrong. She grows fond of him, but the Doctor shields her advances despite having a respect for her, as he does all his companions.