Montrouse Theodore "Trouble" Mouse Junior lives in a tiny, little secret home in the wall of Julianna and Katelyn's house. He's a curious little guy, and that trait often takes him on surprising adventures to dangerous, unknown places. He frequently finds himself facing scary, life-threatening situations for a mouse.

Montrouse ventures out of his house in search of food. Outside of his safe haven, he encounters a number of different situations and experiences with things such as a door, a cat, a mousetrap, air conditioning vent, toilet, and much more. A smart and courageous mouse, Montrouse realizes that although he knows a lot, there is more he can learn.

Despite all of his adventures, he never gives up on himself or on ways to help himself get out of sticky situations.