Sixth-grader Ellen Sugimori just wants to be a normal American kid, one who doesn't have to go to Japanese school every Saturday. First-grader Risako Sugimori wants to be a scientist. Despite Ellen's best efforts, Risako's mysterious prototype machines get the two of them into all sorts of tricky situations.

From crash landings on the surface of Mars to unintended travels through time, from undersea explorations to malfunctioning multiplier machines, getting back home in time for dinner always takes some drastic measures!