Smithers was a scientist who developed the insecticide DN6 in the hopes of ending famine, having spent a lot of time working on it.

When he found out his business partner Forester had murdered government official Arnold Farrow to prevent his negative report on DN6 from being filed, he helped Forester cover up the murder. He turned against Forester when he found out how lethal DN6 was and disarmed Forester, who had had a bomb explode in his face. They were both arrested by PC Bert Rowse. (TV: Planet of Giants).