A class of adolescent schoolchildren are in Niagara Falls touring the hydroelectric power plant connected to the falls. Included in the group are Penny Twidgett and her younger brother Tommy Twidgett. More interested in his yo-yo, Tommy is constantly falling behind the group. One time when Penny stops with him to fix his yo-yo, they lose the rest of the group. Wandering around the power plant on their own, they stumble into a restricted area where they are confronted by the caretaker of that area. Before he leaves to find the rest of their group, the caretaker leaves the two children there by themselves, telling them not to touch anything but especially the handle that will stop the flow of water over Niagara Falls. Tommy being Tommy, he doesn't believe it and pulls the handle. Not only does the water stop flowing over the falls, but the handle breaks off. They are pursued by a security guard who they believe want to put them in jail for what they did. They just want to return the handle to any adult who can help them, but every adult they approach dismisses them since the adults are all dealing with the more important issue of a power outage in the city since no electricity is being generated because the falls stopped.