The Isons were a species of humanoids from Isos. At some point, Isons colonised Isos II. In the 20th century, this planet was invaded by Cyberman, who converted the entire population into Cybermen. (AUDIO: The Isos Network) which attempted to invade Earth via International Electromatics, however these Cybermen were destroyed, (TV: The Invasion) barring one ship.
This single ship travelled back to Isos II, pursued by the Second Doctor. At the same time, Isons from Isos had discovered the loss of the entire colony's population five years earlier, and had arrived to investigate. Together with these Isons, the Doctor, Jamie, and Zoe helped to defeat the Cybermen, destroying them and their ship. (AUDIO: The Isos Network)