Someone in this class is a witch. 

When the note, written in ordinary ballpoint, turns up in the homework books Mr Crossley is marking, he is very upset. For this is Larwood House, a school for witch-orphans, where witchcraft is utterly forbidden. And yet magic keeps breaking out all over the place – like measles!

The last thing they need is a visit from the Divisional Inquisitor. If only Chrestomanci could come and sort out all the trouble.