A mystery illness leaves Topaz the kangaroo without a hop and the vets scratching their heads. When Topaz is taken for treatment, rumours begin to spread around the zoo that it could be 'Uncle Nigel's Hoppitystophop' - a horrible condition that causes kangaroos to lose their ability to hop. Jealous of all the attention on Topaz, hapless gorilla and self-appointed leader of the zoo, Jurgen conjures up an illness in need of treatment of his own. Diagnosed by fellow gorilla Geoffrey as 'attention-seeker-itis'- will he and Topaz ever recover?