Autumn has come - but this year Petronella doesn't have time to help with the apple harvest. She flies to the witch swamps to take part in a big meeting. All the witches who have been awarded the golden witch's plait are invited. What an honour! Lea and Luis are also going on a trip - they are going on a school trip. It soon becomes clear that the castle they are staying in is haunted! When a couple of not-so-nice ghosts lure the twins and their friends into an ambush, things get dicey. But luckily it's not far from the witches' swamps to the haunted castle. And so Petronella is able to rush to the rescue just in time ...