One day, Ivan and his sister discover a very strange egg in the forest. "It is the egg of an ogg," the old man of the forest tells them. "Now leave it be." But the children and their neighbours are curious. What IS an ogg? Will it walk? Will it fly? Will it like cherry pie? Will it sing? Will it dance? Will it hop? Will it prance? But when the egg of an ogg finally hatches, it is stranger and BIGGER than any of them could have imagined. Can the children stop the ogg growing before it flattens the town? And will they ever learn to leave strange things be?