"It's alive!" cries William, holding the moonball.
"How can it be?" asks Gloria. "It doesn't have any mouth, or eyes, or anything! It's just a furry ball."
"But it is alive," William says. "It's licking my hand!"
Ever since the children first found the mysterious moonball, it has made them happy. But now the Professor has taken the moonball away to study it.
He won't give it back!
And that's how the trouble starts.