Nanci Cruz was an American teenager who had recently moved to England. She was betrayed by her best friend and her boy friend. One day as she walked down the street, a boy crashed into her, then healed her physical and emotional pains. He ran off because an old woman was chasing him.
The Second Doctor approached Nanci and told her about the boy's ability to remove pain from others. She helped him search for the boy. That night, she and the Doctor tried to rescue the boy, but while the Doctor was able to get the boy away from the woman, the woman captured Nanci.
The woman offered to trade Nanci for the boy, but then tried to kill Nanci. The boy healed Nanci's pain, then channelled it to the woman, who exploded. Nanci, returning home, realised that she had to learn to live with her pain. (PROSE: Mother's Little Helper)