Third grader and inventor extraordinaire Ada Lace has a new social studies teacher--who loves group projects. While most of the class has constructed regular dioramas with clay and construction paper, Ada, her best friend Nina, and sometimes nemesis Milton have built a complex scale model of an historic silver mine. But when Milton reveals that he added his "old Milton touch" on their project right before turning it in, Ada worries that he has sabotaged their work.

In a desperate attempt to save their project, Ada and Nina use their combined creative and technical prowess to perform a heist and break into their teacher's supply closet after school.

Do the two friends have what it takes to deceive the school's security system? Or will they get caught trying to pull off this seemingly impossible mission.