Eric is an ordinary boy who loves football, and hates tests. Unluckily, a big test is coming up! Then his Auntie Rose sends him a very strange present from her travels in South America: an ugly, stinky, stripy jumper with magical powers. It can turn the wearer into a genius, so long as it is never washed. Eric finds the jumper really does have a miraculous effect on his brain power – but can there be too much of a good thing?