Alex the lion is the king of the urban jungle, the main attraction at New York's Central Park Zoo. He and his best friends -- Marty the zebra, Melman the giraffe and Gloria the hippo -- have spent their whole lives in blissful captivity before an admiring public and with regular meals provided for them. Not content to leave well enough alone, Marty lets his curiosity get the better of him and makes his escape -- with the help of some prodigious penguins -- to explore the world.