Mad scientist Dr Charles Decker (Michael Gough) returns from Africa after it has been presumed for a year that he died in a plane crash.
During his year in Africa, he discovered a method of growing plants and animals to an enormous size. Most conveniently, the potion also puts the receiver under the mental control of the person who administers it to them.
So Decker brings a baby chimpanzee – “Konga” – back with him to test his theory.
Back at his college, Decker ignores the overtures of his assistant Margaret (Margo Johns), cosies up to curvaceous female student Sandra Banks (Claire Gordon) – upsetting Bob (Jess Konrad) who is smitten with Sandra – and argues with Dean Foster who disagrees with Decker’s modern evolutionary claims and basically calls Decker a madman.
Having his tenure threatened, Decker injects Konga with even more of his rapid growth serum. The ape grows to gigantic proportions (and somehow morphs from a chimp to a gorilla!) and heads across campus to kill Dean Foster.
While Decker is a suspect (because his heated argument with the Dean was overheard by Foster’s secretary) the chaps at Scotland Yard release him because they believe they are looking for either an animal or an incredibly strong man.
Holding a cocktail party for friends and faculty members, Decker meets Professor Tagore (George Pastell) who – coincidentally – is conducting almost identical experiments as Decker and is at the point where he is ready to announce his findings to the scientific community.
Determined not to be robbed of glory, Decker later pays Tagore a visit at his laboratory, taking Konga along with him to make sure his point is made. He also decides to use Konga to remove the obstacle between him and the luscious Sandra and has the gorilla kill poor Bob right in front of his own home.
Margaret tells Decker that she is aware of what he is doing but will not go to the police if he agrees to make an honest woman of her. But while Decker is groping and slobbering all over Sandra in his hot and humid greenhouse, Margaret overhears and in a jealous rage, she goes to Konga’s cage and injects him yet again.
The dose is a tad too much, though, and he grows to King Kong size and crashes through the roof of the house, killing Margaret in the process.
Sandra is attacked by a Venus Fly Trap and Konga grabs Decker and heads off to wreak havoc all over London.
Unfortunately, the havoc-wreaking is cut short when Konga is killed by machine-gun fire from the Army who arrive on the scene in minutes.
Hurling Decker to the ground, Konga reverts back to a baby chimp and dies.
Oh well, it’s not every day you get to see a stuntman in a second-hand gorilla costume laying waste to Croydon High Street.
Dr Charles Decker