SULPHUR, LA (KPLC) - Calcasieu Sheriff's investigators are working an armed robbery at a convenience store in Sulphur. It happened around 5:15 Sunday evening at the EZ Mart on Houston River Road. Calcasieu Sheriff's officials say a black female walked into the store armed with a hand gun demanding money. They say she fled with an unknown amount of cash. We'll of course keep you updated on any new developments.