Treh is a mouse like any other. He lives in the countryside, leaves his burrow, looks for food, and coexists with other mice, especially his little brother. One day, something unexpected disrupts their ordinary life: a large fair has set up shop in their habitat. Now, every time they leave their burrow, there are people everywhere: rides, food stalls, and screaming children. All they have to do is adapt to their new environment and look for food in the garbage left behind by the fair.

But oh no... it seems the fair isn't the only new thing around. Ringtails have arrived and, just like mice, they look for food in the piles of rubbish, only these animals don't like to share... In their first encounter, the ringtails try to steal the rubbish, but when they see the mice resist, the ringtail chief kidnaps Treh's little brother for his dinner. Treh can't allow it and runs after him to rescue his little brother, and the three of them head into the great fair where Treh will have to face even more obstacles. Will Treh be able to rescue his little brother in time?