Margaret "Maggie" Cain was a character from the 2009 Doctor Who special "The Waters of Mars". She was the second Bowie Base One colonist to be infected by the Flood. She was played by Sharon Duncan-Brewster.
Born in Sheffield on 28 December 2028, Maggie gained a first honours chemistry degree and went into engineering. She was a British cosmonaut on the Russian Federal Space Agency mission Project Midas, beating over twenty-five thousand other candidates. In 2051, she became the second British woman to walk on the moon. She met the first, Adelaide Brooke, and the two developed mutual respect. Consequently, Brooke asked Cain to join the Bowie Base One mission. She arrived at the base in 2058 and worked there, studying the planet Mars. There, she was infected with a virus, known as the Flood, which changed her body form. With the other infected members, she tried to infect the remaining crew and escape to Earth, but failed, due to the actions of the Tenth Doctor. While infected, she appeared to act as the leader of the Flood infectees. She had a voice powerful enough to crack the ice holding the main body of the Flood.
Maggie perished when Adelaide activated Action Five, setting off a nuclear device in the heart of the base and destroying it along with the Flood.