Constantine (The Empty Child)

Dr Constantine was a physician working in Albion Hospital when it was overcome by the Empty Child plague. Constantine was the last person in the Hospital unaffected by the nanogenes. He was able to lead the Ninth Doctor to the first elements of understanding the plague.

Biography
Constantine worked at the hospital during the Blitz, and one night a patient brought before him was Jamie. He tried some experimental therapy with the 'empty' child in Room 802 and recorded it - his empathy likely due to the fact he had lost his own children and grandchildren to the war. Over time every other person in the hospital was infected, first doctors and nurses, then patients. Constantine continued to take care of them nonetheless and at least kept them comfortable, but feared that the Army would simply bomb the place and blame it on the Germans, as other cases were appearing outside the hospital, all over London.

By the time the Doctor arrived Constantine himself was the only one left unchanged by the plague, though already showing symptoms (such as a scar on his hand). His presence seemed to keep the gas mask zombies subdued, possibly because their childlike mentality recognised the doctor's authority.

Constantine invited the Doctor to examine the patients around him, and explained how the same symptoms spread. He tried to explain to the Doctor about Nancy's knowledge of events before he succumbed to the plague himself and became a gas mask zombie like the others. He then proceeded to threaten the Doctor, Rose Tyler and Captain Jack Harkness when Jamie found Nancy again. The Doctor was able to keep them at bay by 'sending them to their room', probably to the same effect that Constantine's authorative presence had on the others before changing.

He would be among the victims of the plague summoned to the crash site of the Chula ship. When the nanogenes later recognised the correct human DNA, they repaired all those who had been infected, restoring Constantine, who was then able to carry on his good work at the hospital. (DW: The Empty Child / The Doctor Dances)