Astrid, The Au-Pair From Outer Space

When Harry's mum tells him they are going to get an au pair, he isn't quite sure what it means. When he finds out it's a girl to help look after him and baby brother, Fred, he feels a bit suspicious. It might just be a good excuse for the school bully to tease him. However, he soon warms to Astrid when she turns up and especially when she gives him an idea that stops the bully from ever bothering him again.
All the same, Harry can't help wondering why Astrid's never heard of tin openers or Coke, and how come her suitcase can move around by itself...