Cathy's birthday's on 29th February, which is an impossible day as it is, because it's a leap day. Then her dad comes up with the bright idea of giving her a duck egg to hatch for her tenth birthday. The chick appears when Cathy and her best friend Margot are watching, and the chick thinks Margot is its mummy. But Margot is bound to a wheelchair and will soon have to go to a special home. Unable to look after the duckling on her own, her parents decide to ged rid of it... Cathy and Margot end up in an adventure which teaches them a lot about how to rescue a migratory bird, but even more about themselves.