Meet Arlo, a young boy who loves writing lists, dinosaurs and his best friends. Arlo and his friends are in Class 4X – a class with a reputation for scaring away teachers. Things aren't looking good, another teacher has run away screaming (literally). When the new substitute teacher, Mrs. Ogg, arrives Arlo wonders how long she will survive. Mrs. Ogg takes the class on a school trip, and the head teacher warns everyone to behave or they can’t go to the end-of-year party! Arlo realizes it's up to him to keep everyone in line. What Mrs. Ogg fails to mention is that they’re going to no ordinary zoo. . .