Frank Hartley

 was the son of Mr Hartley and the brother of Yvonne Hartley. He wished to be called up to the work crews who were breaking through the city roof to the surface of Mondas but he wasn't because he was too young and Mr Hartley wouldn't let him go. After he realised what had happened to his sister and those who were called up, he helped the Fifth Doctor and Nyssa destroy the Cybermen. (AUDIO: Spare Parts)