The story begins with a mysterious egg washed up on a Scottish beach, the morning after a great storm.
Kirstie and her brother Angus find the egg and take it home. The next day it has hatched into a tiny greeny-grey creature with a horse's head, warty skin, four flippers and a crocodile's tail.
The baby sea monster soon becomes the family pet - but the trouble is, it just doesn't stop growing!
About the Author
Dick King-Smith is one of the best-loved children's authors of today. He has written over a hundred books, including The Sheep-Pig, winner of the Guardian Fiction Prize, which inspired the blockbuster film Babe.