A group of delinquents led by Fred (Beau Bridges) turn up in a small town. In that town Mike (Tommy Kirk) is trying to make out with his girlfriend (Charla Doherty) when little Genius (Ron Howard) invents a weird orange goo which turns animals into giants.
Naturally its not long before Fred and his gang take the goo themselves and become giants who terrorise the town. Normal size teens and adults are at their mercy...
Now, it doesn't sound very promising, the special effects and acting are not up to much and most of the characters are hard to warm to. However, despite that the film is great fun, maybe because it is just so ridiculous.