Living in an underground city on the Moon, Holly and Jeff's hobby is flying with strap-on wings in a great cavern, made possible because the gravity field is one sixth the strength of Earth's and the air pressure in the cavern is kept high enough. Ariel wants to try flying, and Holly, in order not to appear jealous, offers to teach her. However, during her first flight, Ariel loses control at a great height, falling toward the ground. Holly swoops down and saves her life, breaking both arms in the process as she cushions Ariel's fall.