A sneaky 'big egg' swap leads to a hairy and hilarious hunt for the real thing! When Mrs Stigson the Stegosaurus lays an egg there is great rejoicing - Darwin always wanted a baby sister. But leaving mad Uncle Loops in charge of egg-sitting is not a good idea. On her return, Mrs Stigson is certain that it is not the egg she laid. Darwin is determined to get to the bottom of it and suspects a certain gangster T-rex is behind the swap. But which is the 'real' Stegasaurus egg? And what will stop Flint Beastwood from smashing it on his wedding day? Jeanne Willis's madcap characters and story, with Arthur Robins' inspired illustration, are certain to tickle anyone's funny-bone!