MITCHELL, S.D. (MITCHELLNOW) A deadly crash involving an underage driver is under investigation in Gregory County. The Department of Public Safety says it happened on U.S. Highway 18, about four miles west of Gregory. A 15-year-old passenger was killed, and the 15-year-old driver suffered serious injuries. Authorities said they  believe the driver lost control in a construction zone, went into a ditch, and rolled. The cause of the crash is still being investigated. For more crime stories from MitchellNow.com, click here.