Guerrilla (The Day of the Daleks)
Talk about it here.
A guerrilla fought against the Daleks in an alternative 22nd century. Using stolen Dalek plans, a time machine had been built so he could travel back in time to Auderly House in the 1970s and kill Sir Reginald Styles, the person assumed to have started escalations into World War III.
One night, the guerrilla tried to kill Sir Reginald but failed. The next day, when he tried to return home, he was attacked and left for dead by two Ogrons that had followed him.
After UNIT troops found his body, Captain Yates had Sergeant Benton escort him to a hospital. While in the ambulance, the Third Doctor meddled with his time machine, which appeared to bring the guerrilla back to his home era. Later, when Jo Grant threatened to destroy his time machine, Anat claimed that his body had been found there. (TV: Day of the Daleks)