The boy was someone who could take away another person's pain. One day he ran into Nanci Cruz, knocking her down. He took away her pain, but ran off as an old woman chased after him. She wanted his abilities for herself and had placed a box on a strap across his chest, which she controlled with another box.
After he was captured by the woman, Nanci and the Second Doctor tried to rescue him. The Doctor managed to get him away, but Nanci was captured by the woman. The woman proposed to trade the boy for Nanci, but when she tried to kill Nanci, the boy took away Nanci's pain and channelled it to the woman, who exploded.