Is Area 51's cover blown? Sky and her otherworldly friends scramble to protect its secrets when a UFO goes missing in the fourth installment of this laugh-out-loud, Edgar Award-nominated series for young readers. For the first time since Sky got to Area 51, things seem to be under control. No bunker hideouts. No incoming space toilets. No kidnappings of beloved relatives. In fact, everyone is in a celebratory mood because a special...