Nelly and Valle have become masters at handling monsters and other dangers looming, always strictly following their three principles: knowledge, cunning and calm. But is this the right approach if you want to teach three tired school ghosts to read and count?
Nelly and Valle are on a cycling holiday. Their teacher from the Monster Academy has tipped them to set camp near an old school. The camp looks idyllic, but at night they can hear loud screams coming from the old school. Frightened but curious, they decide to investigate and go in the school. They are greeted there by a strange sight: an old ghost tries to teach three mischievous ghosts to read and count. He says that this is his very last mission before he can have peace.
Nelly and Valle realize that they have to help him, and the ghost lets them gratefully take over the teaching. They begin by giving the ghosts some responsibilities and they will then use all their cunning and wits to be successful in their mission.
This is the seventeenth adventure featuring Nelly Rapp, a fun, slightly scary and easy-to-read series.