Mark was a guerrilla fighter and a member of the human resistance opposing the Daleks from an alternative 22nd century Earth.
Mark, Anat, Boaz, Monia and several other resistance fighters took part in an attack on the Controller's compound to rescue the Third Doctor and Jo Grant. However, Mark, along with Boaz, was a casualty of the mission, being shot and killed by a Ogron. (TV: Day of the Daleks)