He can change into animals. All sorts of animals: a flea, a pigeon, even a rhino.
Trouble is, he can't decide when - it only happens when he gets worried. And right now, Charlie has quite a lot to worry about:
His brother (who is in hospital)
His parents (who are panicking about it)
And the school bully (who has Charlie in his sights)
And even though every kid wants a superhero power, Charlie isn't keen on changing into a chicken in the middle of the school play.