Around Halloween, strange things are always happening in the town where Nelly and Valle live. This year, the two agents have received a mission from the Monster Academy to find out why.

This particular night, the Halloween swim meet is taking place, and the oddities are soon piling up! The water turns to slime, the trampoline is as soft as cooked spaghetti, and a huge shark suddenly appears in the pool. There is definitely something supernatural going on. Could Nelly and Valle’s classmate Bim have something to do with it?