Another series created by pre-eminent special-effects man Gerry Anderson - although Anderson didn't work on this as closely as his other series, since Thunderbird 6 and Doppelgänger were taking up more of his time - hence David Lane served as producer with Reg Hill as executive producer. (However, Gerry Anderson did co-write "The Most Special Agent" with Sylvia Anderson, and "Operation McClaine" with David Lane.)
The series follows Joe McClaine, a 9-year-old British schoolboy, the adopted son of Professor Ian "Mac" McClaine, a renowned computer expert. Residing in a secret underground laboratory is Mac's latest invention, the "BIG RAT" (Brain Impulse Galvanoscope Record and Transfer), a machine capable of recording knowledge and experience from leading experts in various fields and transferring it to another human brain. The central aspect of the design is the "Rat Trap", a rotating spherical cage in which a subject is seated during the transfer of the expert "brain pattern".
Sam Loover, a secret agent for the World Intelligence Network, persuades Mac, his friend, to dedicate the BIG RAT to WIN's pursuit of world peace by permitting Joe to assume such knowledge and experience and become a WIN agent. After the requisite skill is transferred, and provided that Joe is wearing special spectacles containing hidden electrodes storing the expertise, he is able to execute such missions as operating fighter aircraft, blasting off into space and performing advanced neurosurgery, all the while appearing to be an innocent schoolboy to the enemies of WIN. Since no one would usually suspect a child of espionage, Joe is WIN's "Most Special Agent". Reporting to the commander-in-chief of WIN's London Headquarters, Shane Weston, he is also provided with a special briefcase, which on superficial inspection appears to be a simple school case but in fact conceals an adapted handgun and WIN transceiver.
In a manner similar to other Gerry Anderson series, Joe 90 features gadgets, rescue operations, secret organisations, and criminal and terrorist threats to the safety of the world. A recurring foe for WIN is the "Eastern Alliance", which dominates Asia. Despite the 9-year-old protagonist, Joe 90 was not aimed at a particularly younger audience than Anderson's two previous series, Thunderbirds and Captain Scarlet and the Mysterons. In fact, like its direct predecessor it features some of the grimmest stories of any Supermarionation series, and Joe regularly kills people and is threatened himself.
Joe 90 provides examples of the following tropes:
- All Just a Dream: "The Race" and "Lone-Handed 90." Technically, the first episode as well, "The Most Special Agent" — the mission Joe undertakes in this one takes place in Sam Loover's mind, as he illustrates to Professor McClaine how Joe and the BIG RAT could be useful. The Professor understandably doesn't like putting his son in danger at first.
- Birthday Episode: One of these doubled as the Grand Finale as the characters celebrated Joe's birthday.
- Clip Show: "The Birthday".
- Expospeak Gag: The title sequence proclaims it to be filmed "In Videcolor" and "Supermarionation". Plain English translation: "It's in colour, and it's a (sophisticated) puppet show."
- Fun with Acronyms
- Hair of Gold, Heart of Gold: Joe. He's good-hearted, wholesome and definitely young.
- Imagine Spot: As mentioned, the whole first episode, where Weston explains the kind of adventure Joe could have, sneaking into a Soviet airbase and stealing a Mig-242. Then at the end, apropos of nothing, he says there is no such plane and no conflict with Soviet Russia.
- Kid Hero: The main character, Joe McClaine.
- Pungeon Master: Shane Weston loves these — even his name is a pun.
- Neural Implanting: What the BIG RAT does to give the knowledge and experience to the one it is being used on.
- Rescue: Some of Joe’s missions involve rescues.
- Refuge in Audacity: Whenever anyone asks Joe what he's been doing during the absences caused by his missions he tells them the truth, secure in the knowledge that they'll think he's making it up.
- Techno Wizard: Professor Ian McClaine.
- Teen Superspy: Pre-teen superspy actually, as Joe is only 9 (until "The Birthday," that is).
- 20 Minutes into the Future: The series was set in a future era (counting from the 1960s), probably 2012-13.
- When Things Spin, Science Happens: The Rat Trap spins rapidly while Joe's sitting inside it receiving his latest brain pattern.
- Wise Beyond Their Years: Justified - Joe uses the BIG RAT to instantly gain whatever knowledge or skills he needs for a mission, and only keeps this knowledge/skills for a single episode. Without the BIG RAT, he isn’t much smarter than an average nine-year-old.