Before leaving the underground aircraft plant to trail Carla Davis, their only lead in the mystery of the wailing witch, Hop and Tank witnessed a wind tunnel test of the fourth experimental model. Standing in the master control room, they watched as Gore opened the throttle controlling the giant wind motors, and the air stream roared against the model at a speed of more than seven hundred miles per hour. Suddenly, the plane began to buck, and was flung against the far wall!