Gone were the overtly hi-tech hardware and more traditionally epic heroics of previous Anderson outings, to be replaced by the smaller scaled secret agent adventures of a bespectacled nine-year-old schoolboy named Joe McClain, who was the adopted son of brilliant electronics genius, Professor Ian McClaine, creator of the BIG RAT device, (Brain Impulse Galvanoscope Record And Transfer), a technologically sophisticated device which recorded the brain patterns and special skills of one person and transferred them to another. At the suggestion of Shane Weston, Deputy Head of the World Intelligence Network, McClaine subjected Joe to the BIG RAT treatment, successfully transferring to the boy the specialist knowledge and attributes of an appropriate highly skilled adult, thereby making him WIN's "Most Special Agent".

At the outset of each mission, Joe would be placed in a special chair that rose up into a circular cage which revolved as the BIG RAT tape containing the chosen specialist's brain patterns was run and fed directly into the boy's mind. Once the transfer was complete, Joe would don a pair of 'electrode glasses' to trigger the new knowledge housed within him. Over the course of the series, his missions called upon him to adopt the personas of such diverse experts as an astronaut, test pilot, racing driver, aquanaut, computer boffin and a brain surgeon.

Among the well known vocal talents behind the characters were those of TV's original 'Maigret, Rupert Davies, and Keith Alexander, the voice of another 1960s puppet celebrity - Topo Gigio. Clearly the most child oriented of the latter Anderson Supermarionation series, 'Joe 90's' appeal with the adult section of the audience which had been captured by 'Thunderbirds' and its follow up series 'Captain Scarlet', suffered from the decision to make the all important central character a child. While still enjoyable and technically accomplished, ultimately 'Joe 90' is remembered as one of the Anderson stable's lesser series.